Changes

xua,tcp-m3ua: Unify Rx code paths to deduplicate code

This also makes those protocol paths resembles more the one of IPA,
where we call rx_ipa_msg() to handle the msgb.

m3ua_tcp_cli_read_cb() is also modified to avoid going through the SCTP
read_cb, which doesn't make much sense.

Change-Id: I54cf6c9b8c27fd67bae74d7931745f140e0575c0