Extend tunnel support to MPLS over IPv4.  The implementation extends the
existing differentiation between IPIP and IPv6 over IPv4 to also cover MPLS
over IPv4.
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Dinan Gunawardena <dinan.gunawardena@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>