tipc: Standardize error checking on incoming messages via native API

This patch re-orders & re-groups the error checks performed on
messages being delivered to native API ports, in order to clarify the
similarities and differences required for the various message types.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>