IB/mlx4: Add support for blocking multicast loopback QP creation user flag

MLX4_IB_QP_BLOCK_MULTICAST_LOOPBACK is now supported downstream.

In addition, this flag was supported only for IB_QPT_UD, now, with the
new implementation it is supported for all QP types.

Support IB_USER_VERBS_EX_CMD_CREATE_QP in order to get the flag from
user space using the extension create qp command.

Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>