Description of problem:
ethmonitor generates "WARNING Interface XXX does not exist" at every monitor operation.

The issue occurs when the interface doesn't have an IP address.

is_interface() in ethmonitor script uses 'ip -a -o inet addr show' command.
The command shows interfaces which have IP addresses.
On the other hand, if the interface belongs to (OVS/Linux) bridge.
The physical/bonding interfaces don't have IP addresses.

To detect the correct interface in that situation, we should backport the following commits into RHEL8.2 and RHEL8.4.

~~~
commit 40d05029ce0b2ad437377cf9a8bcb4c91508fa89
Author: Heitor R. Alves de Siqueira <halves>
Date:   Thu Mar 21 16:29:33 2019 -0300

    ethmonitor: check if interface exists by link
---
commit c0ac191c73f1a3cf62d54b7ec59992997cca3810
Author: Heitor Alves de Siqueira <halves>
Date:   Wed Apr 17 17:16:39 2019 -0300

    ethmonitor: fix is_interface() regression
    
    Commit 40d05029ce0b changed is_interface() to list by link instead of
    address. We need to adjust the grep filter for the new output format,
    else we'll miss interfaces.
---
commit 7f7ca75100a846242ff1510fd9bcf299cd3d00eb
Author: Aleksei Burlakov <aleksei.burlakov>
Date:   Mon Oct 26 13:25:45 2020 +0100

    ethmonitor: is_interface: RE matches vlan names
    
    Vlan names end not with : but are suffixed with the @devices-name
~~~

Version-Release number of selected component (if applicable):
resource-agents in RHEL8.2 and RHEL8.4.


How reproducible:
Everytime when ethmonitor's monitor operation runs.

Steps to Reproduce:
1. Configure an interface which belongs to ovs-bridge.
2. Setup ethmonitor for the bonding device which doesn't have an IP address.
3. Observe the error message is shown.

Actual results:
The warning message is shown

Expected results:
The warning message is not shown.

Additional info:
The message makes user confused. We should prevent it.