Merge branch 'ip6_tunnel-add-MPLS-support'

Vadim Fedorenko says:

====================
ip6_tunnel: add MPLS support

The support for MPLS-in-IPv4 was added earlier. This patchset adds
support for MPLS-in-IPv6.

Changes in v2:
- Eliminate ifdefs IS_ENABLE(CONFIG_MPLS)
====================

Signed-off-by: David S. Miller <davem@davemloft.net>