IB/uverbs: Enable QP creation with a given source QP number

Enable QP creation with a given source QP number, the created QP will
use the source QPN as its wire QP number.

To create such a QP, root privileges (i.e. CAP_NET_RAW) are required
from the user application.

This comes as a pre-patch for downstream patches in this series to
allow user space applications to accelerate traffic which is typically
handled by IPoIB ULP.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>