[NETFILTER]: ip6_tables: support MH match

This introduces match for Mobility Header (MH) described by Mobile IPv6
specification (RFC3775). User can specify the MH type or its range to be
matched.

Signed-off-by: Masahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: Yasuyuki Kozakai <kozakai@linux-ipv6.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>