datapath: backport: udp: prevent skbs lingering in tunnel socket queues

datapath: backport: udp: prevent skbs lingering in tunnel socket queues

Upstream commit:
    commit e5aed006be918af163eb397e45aa5ea6cefd5e01
    Author: Hannes Frederic Sowa <hannes@stressinduktion.org>

    udp: prevent skbs lingering in tunnel socket queues

    In case we find a socket with encapsulation enabled we should call
    the encap_recv function even if just a udp header without payload is
    available. The callbacks are responsible for correctly verifying and
    dropping the packets.

    Also, in case the header validation fails for geneve and vxlan we
    shouldn't put the skb back into the socket queue, no one will pick
    them up there.  Instead we can simply discard them in the respective
    encap_recv functions.

    Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
Acked-by: Jesse Gross <jesse@kernel.org>