[subintf & mirror] Mirror monitor port via a local sub port router interface

[wendani]

What I did
Deal with the possibility that the chosen next hop object goes through a local sub port router interface

Why I did it
Mirror destination lookup is done in default VRF. As a sub port router interface can be the local router interface of the next hop or next hop group member of an ip prefix in default VRF, here we deal with such a likelihood.

How I verified it
Newly added vs tests:

• Mirror session add removal, together with the following update event MirrorOrch observes:
  • ip prefix removal and add
  • neighbor mac update
  • lag member removal and add
  • lag member status change (depends on [mirror] Observe lag member status change #1846)
• Mirror session status update at parent port oper status change for the case of mirror destination in directly connected subnet (depends on [mirror] Update session status at port oper status change for mirror destination in directly connected subnet case #1725)
  • neighbor mac update
  • neighbor mac removal and add
• Next hop group update on LPM ip prefix that causes monitor port (Mirror to port) to migrate from via a local sub port router interface to via other local RIFs, and vice versa. Validate a local RIF migrated to/back from being one of the following types:
  • EthernetX
  • PortChannelX
  • Vlan interface of the same vlan id
  • Vlan interface of a different vlan id
  • EthernetX.Y sub port interface
  • PortChannelX.Y sub port interface
• LPM ip prefix update that causes monitor port (Mirror to port) to migrate from via a local sub port router interface to via other local RIFs, and vice versa. Validate a local RIF migrated to/back from being one of the types listed above.
• ERSPAN ipv6 encap (depends on [mirror] erspan ipv6 underlay #1817)

Details if related
Contains (dependency on) #1725

[prsunny]

Test failures?