vxlan: Correct path typo in comment

Flags are used in the return path rather than the return patch.

Fixes: af33c1ad

 ("vxlan: Eliminate dependency on UDP socket in transmit path")
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>