RDMA/rxe: Fix skb lifetime in rxe_rcv_mcast_pkt()

RDMA/rxe: Fix skb lifetime in rxe_rcv_mcast_pkt()

The changes referenced below replaced sbk_clone)_ by taking additional
references, passing the skb along and then freeing the skb. This
deleted the packets before they could be processed and additionally
passed bad data in each packet. Since pkt is stored in skb->cb
changing pkt->qp changed it for all the packets.

Replace skb_get() by sbk_clone() in rxe_rcv_mcast_pkt() for cases where
multiple QPs are receiving multicast packets on the same address.

Delete kfree_skb() because the packets need to live until they have been
processed by each QP. They are freed later.

Fixes: 86af61764151 ("IB/rxe: remove unnecessary skb_clone")
Fixes: fe896ceb5772 ("IB/rxe: replace refcount_inc with skb_get")
Link: https://lore.kernel.org/r/20201008203651.256958-1-rpearson@hpe.com
Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>