RDMA/rxe: Fix coding error in rxe_rcv_mcast_pkt

rxe_rcv_mcast_pkt() in rxe_recv.c can leak SKBs in error path code. The
loop over the QPs attached to a multicast group creates new cloned SKBs
for all but the last QP in the list and passes the SKB and its clones to
rxe_rcv_pkt() for further processing. Any QPs that do not pass some checks
are skipped.  If the last QP in the list fails the tests the SKB is
leaked.  This patch checks if the SKB for the last QP was used and if not
frees it. Also removes a redundant loop invariant assignment.

Fixes: 8700e3e7 ("Soft RoCE driver")
Fixes: 71abf20b ("RDMA/rxe: Handle skb_clone() failure in rxe_recv.c")
Link: https://lore.kernel.org/r/20210128174752.16128-1-rpearson@hpe.com


Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>