RDMA/nes: Cleanup warnings

Wrap NES_DEBUG and assert macros with do while (0) to avoid ambiguous
else.  No one is using sk_buff * returned from form_cm_frame(), so
drop the return.  drop_packet() should not be incrementing reset
counter on receiving a FIN.

Signed-off-by: Chien Tung <chien.tin.tung@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>