Description of problem:
Boot VM with vhost-user server mode, seems the option usage has changed from "server" to "server=on" 

Version-Release number of selected component (if applicable):
qemu-kvm-5.2.0-5.scrmod+el8.4.0+9783+7f5b6b81.wrb210203.x86_64
libvirt-7.0.0-3.scrmod+el8.4.0+9783+5765bd69.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Boot OVS

# ovs-vsctl show
d96517fa-c587-42e7-a4f1-97e4bd488ffb
    Bridge ovsbr0
        datapath_type: netdev
        Port vhost-user0
            Interface vhost-user0
                type: dpdkvhostuserclient
                options: {vhost-server-path="/tmp/vhostuser0.sock"}
        Port dpdk0
            Interface dpdk0
                type: dpdk
                options: {dpdk-devargs="0000:5e:00.0"}
        Port ovsbr0
            Interface ovsbr0
                type: internal
    Bridge ovsbr1
        datapath_type: netdev
        Port vhost-user1
            Interface vhost-user1
                type: dpdkvhostuserclient
                options: {vhost-server-path="/tmp/vhostuser1.sock"}
        Port dpdk1
            Interface dpdk1
                type: dpdk
                options: {dpdk-devargs="0000:5e:00.1"}
        Port ovsbr1
            Interface ovsbr1
                type: internal


2. Boot VM with vhost-user server, successfully.

    <interface type="vhostuser">
      <mac address="18:66:da:5f:dd:02" />
      <source mode="server" path="/tmp/vhostuser0.sock" type="unix" />
      <model type="virtio" />
      <driver ats="on" iommu="on" name="vhost" queues="4" rx_queue_size="1024" />
      <address bus="0x6" domain="0x0000" function="0x0" slot="0x00" type="pci" />
    </interface>
    <interface type="vhostuser">
      <mac address="18:66:da:5f:dd:03" />
      <source mode="server" path="/tmp/vhostuser1.sock" type="unix" />
      <model type="virtio" />
      <driver ats="on" iommu="on" name="vhost" queues="4" rx_queue_size="1024" />
      <address bus="0x7" domain="0x0000" function="0x0" slot="0x00" type="pci" />
    </interface>


3. Check libvirt log, there are warning info: "warning: short-form boolean option 'server' deprecated". Please see below.

...
2021-02-07 08:16:02.443+0000: Domain id=1 is tainted: high-privileges
qemu-kvm: -chardev socket,id=charmonitor,fd=36,server,nowait: warning: short-form boolean option 'server' deprecated
Please use server=on instead
qemu-kvm: -chardev socket,id=charmonitor,fd=36,server,nowait: warning: short-form boolean option 'nowait' deprecated
Please use wait=off instead
qemu-kvm: -chardev socket,id=charnet1,path=/tmp/vhostuser0.sock,server: warning: short-form boolean option 'server' deprecated
Please use server=on instead
qemu-kvm: -chardev socket,id=charnet2,path=/tmp/vhostuser1.sock,server: warning: short-form boolean option 'server' deprecated
Please use server=on instead
2021-02-07T08:16:02.510649Z qemu-kvm: -chardev socket,id=charnet1,path=/tmp/vhostuser0.sock,server: info: QEMU waiting for connection on: disconnected:unix:/tmp/vhostuser0.sock,server
2021-02-07T08:16:02.983951Z qemu-kvm: -chardev socket,id=charnet2,path=/tmp/vhostuser1.sock,server: info: QEMU waiting for connection on: disconnected:unix:/tmp/vhostuser1.sock,server
char device redirected to /dev/pts/1 (label charserial0)


Actual results:
Warning info shows.

Expected results:
There should be no warning info.

Additional info:
1. Qemu usage change causes this warning. Libvirt should adjust itself to qemu accordingly.

(1) Boot qemu with vhost-user "server", it prints "warning: short-form boolean option 'server' deprecated. Please use server=on instead" 

# /usr/libexec/qemu-kvm -chardev socket,id=charnet2,path=/tmp/vhostuser1.sock,server
qemu-kvm: -chardev socket,id=charnet2,path=/tmp/vhostuser1.sock,server: warning: short-form boolean option 'server' deprecated
Please use server=on instead
qemu-kvm: -chardev socket,id=charnet2,path=/tmp/vhostuser1.sock,server: info: QEMU waiting for connection on: disconnected:unix:/tmp/vhostuser1.sock,server

(2) Boot qemu with vhost-user "server=on", it works well.

# /usr/libexec/qemu-kvm -chardev socket,id=charnet2,path=/tmp/vhostuser1.sock,server=on
qemu-kvm: -chardev socket,id=charnet2,path=/tmp/vhostuser1.sock,server=on: info: QEMU waiting for connection on: disconnected:unix:/tmp/vhostuser1.sock,server


2. Qemu version changes
qemu-kvm-5.2.0-5.module+el8.4.0+9775+0937c167.x86_64              still "server"
qemu-kvm-5.2.0-5.scrmod+el8.4.0+9783+7f5b6b81.wrb210203.x86_64    need "server=on"

3. I would assume this warning should be fixed by Libvirt component. If not, feel free to switch to qemu component. Thank you.