T6222: VRRP show prefix for long rfc3768-compatibility interfaces

If we use rfc3768-compatibility with long interface names like
eth1.100.200 it converts the VRRP interface name name
to `<interface>v<VRID><IP version>`
For example `eth2.100.200v10v4`

The limit for interface name is 15 symbols and it causes that
interface name is ignoring by keepalived

VMAC interface name 'eth2.100.200v10v4' too long or invalid characters - ignoring
And it uses the default prefix `vrrp` for such cases.
It works fine, but such interfaces are not displayed in the op-mode

Allow prefix `vrrp` for the op-mode for `show interfaces`

python/vyos/ifconfig/section.py

@@ -97,7 +97,7 @@ def _intf_under_section (cls,section='',vlan=True):
 
         for ifname in interfaces:
             ifsection = cls.section(ifname)
-            if not ifsection:
+            if not ifsection and not ifname.startswith('vrrp'):
                 continue
 
             if section and ifsection != section: