RDMA/rxe: Remove useless code in rxe_recv.c

RDMA/rxe: Remove useless code in rxe_recv.c

In check_keys() in rxe_recv.c

	if ((...) && pkt->mask) {
		...
	}

always has pkt->mask non zero since in rxe_udp_encap_recv() pkt->mask is
always set to RXE_GRH_MASK (!= 0).  There is no obvious reason for this
additional test and the original intent is lost. This patch simplifies the
expression.

Fixes: 8b7b59d030cc ("IB/rxe: remove redudant qpn check")
Link: https://lore.kernel.org/r/20210127224203.2812-1-rpearson@hpe.com
Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>