tipc: Reject payload messages with invalid message type

Adds check to ensure TIPC sockets reject incoming payload messages
that have an unrecognized message type.

Remove the old open question about whether TIPC_ERR_NO_PORT is
the proper return value.  It is appropriate here since there are
valid instances where another node can make use of the reply,
and at this point in time the host is already broadcasting TIPC
data, so there are no real security concerns.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>