IB/rxe: Don't check for null ptr in send()

pkt->qp was already dereferenced earlier in the function.

Fixes Smatch complaint:
drivers/infiniband/sw/rxe/rxe_net.c:458 send()
	 warn: variable dereferenced before check 'pkt->qp' (see line 441)

Signed-off-by: Andrew Boyer <andrew.boyer@dell.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>