When receiving an stun packet on a socket, and looking for the matching
local candidate, normally it doesn't make a difference to test the
address or the base address. Because a pair cannot have a local candidate
of type srv-rflx, where there would be a difference, the local candidate
obtained will be part of a pair of the conncheck list.

Except for the case of a pairs with tcp-act local candidate, where the
addr has a port number of zero (tcp-act socket before connect), and the
socket of the stun packet has a non-null port number (tcp-act socket
after connect), corresponding to the base address of another
peer-reflexive tcp-act local candidate, previously discoverd.

The selection of the local candidate concerned by an inbound stun
request happens when early incoming checks are processed, and when
inbound stun packets are normally received during the conncheck.

This commit complete commit e6a19418 (for early incoming checks)
in the normal inbound stun packets code path, where is similar
modification is needed.