netfilter: nf_conntrack: restrict NAT helper invocation to IPv4

The NAT helpers currently only handle IPv4 packets correctly. Restrict
invocation of the helpers to IPv4 in preparation of IPv6 NAT.

Change-Id: I13c7c924d461e2dce9faa34ec47716aca881a1bc
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
6 files changed