net/smc: restructure CDC message reception

This patch moves a CDC sanity check from smc_cdc_msg_recv_action() to
the other sanity checks in smc_cdc_rx_handler(). While doing this, it
simplifies smc_cdc_msg_recv() and removes unneeded function parameters.

Signed-off-by: Hans Wippel <hwippel@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>