datapath: return an error instead of doing BUG_ON()

datapath: return an error instead of doing BUG_ON()

Upstream commit:
    commit a734d1f4c2fc962ef4daa179e216df84a8ec5f84
    Author: Eelco Chaudron <echaudro@redhat.com>
    Date:   Thu May 2 16:12:38 2019 -0400

    net: openvswitch: return an error instead of doing BUG_ON()

    For all other error cases in queue_userspace_packet() the error is
    returned, so it makes sense to do the same for these two error cases.

    Reported-by: Davide Caratti <dcaratti@redhat.com>
    Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
    Acked-by: Flavio Leitner <fbl@sysclose.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>