Description of problem:

I added some ipv6 addresses with custom masks to a network interface
# ip a
....
    inet6 b023::75/75 scope global 
       valid_lft forever preferred_lft forever
    inet6 b023::71/71 scope global 
       valid_lft forever preferred_lft forever

but after profile sync it has wrong netmasks in its profile:
# rhn-profile-sync 

System > Details > Hardware
Interface	IPv6 Address	Netmask
ens3	b023::71	73
ens3	b023::75	69


and on Fedora 26 rhn-profile-sync does not work because netifaces output has changed
>>> import netifaces
>>> interfaces = netifaces.interfaces()
>>> for interface in interfaces:
...   netifaces.ifaddresses(interface)[netifaces.AF_INET6]
... 
[{'addr': '::1', 'netmask': 'ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff/128'}]
[{'addr': '2620:52:0:2224:5054:ff:fe87:ced6', 'netmask': 'ffff:ffff:ffff:ffff::/64'}, {'addr': 'fe80::5054:ff:fe87:ced6%ens3', 'netmask': 'ffff:ffff:ffff:ffff::/64'}]

# rhn-profile-sync 
Updating package profile...
Updating hardware profile...
Error reading network interface information: <class 'ValueError'>

Traceback (most recent call last):
  File "/usr/sbin/rhn-profile-sync", line 59, in <module>
    cli.run()
  File "/usr/share/rhn/up2date_client/rhncli.py", line 96, in run
    sys.exit(self.main() or 0)
  File "/usr/sbin/rhn-profile-sync", line 50, in main
    rhnHardware.updateHardware()
  File "/usr/share/rhn/up2date_client/rhnHardware.py", line 10, in updateHardware
    hardwareList = hardware.Hardware()
  File "/usr/share/rhn/up2date_client/hardware.py", line 941, in Hardware
    ret = read_network_interfaces()
  File "/usr/share/rhn/up2date_client/hardware.py", line 741, in read_network_interfaces
    netmask_bits += 16 - 1 - bin(int(two_octets, 16))[2:].rindex('1')
<class 'ValueError'>: invalid literal for int() with base 16: 'ffff/128'


Version-Release number of selected component (if applicable):
rhn-client-tools-2.7.11-1.fc26.noarch

How reproducible:
always

Steps to Reproduce:
1. add ipv6 address with custom mask
2. rhn-profile-sync
3. check System > Details > Hardware