vxlan: Correctly set flow*i_mark and flow4i_proto in route lookups

VXLAN must provide the skb mark and specifiy IPPROTO_UDP when doing
the FIB lookup for the remote ip. Otherwise an invalid route might
be returned.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>