pgw: Expect EchoResp in CLIENT port of component who sent EchoReq

A recent commit in GTPv2_Emulation improved the routing of incoming
messages from network towards clients.
After that change, the GTPv2_Emulation properly matches the originating
component of the procedure and forwards the reply to it.
Hence, TC_tx_echo() needs to be adapter to expect the reply on its
CLIENT port.
TEID0 is now left for incoming initiating messages which have no seqnr
match.

Change-Id: I1764fdf81192597e393d79d34cb8f221aa79bbd9
Fixes: 1d2cc67036e95a0c3ee3ac7738d7e15d5f76b8a2
1 file changed