IB/rxe: avoid double kfree skb

In rxe_send, when network_type is not RDMA_NETWORK_IPV4 or
RDMA_NETWORK_IPV6, skb is freed and -EINVAL is returned.
Then rxe_xmit_packet will return -EINVAL, too. In rxe_requester,
this skb is double freed.
In rxe_requester, kfree_skb is needed only after fill_packet fails.
So kfree_skb is moved from label err to test fill_packet.

Fixes: 5793b465

 ("IB/rxe: remove unnecessary skb_clone in xmit")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>