linux-cp: stop managing adjacencies for tunnels

linux-cp: stop managing adjacencies for tunnels

Type: fix

Outbound packets which arrive on tun/L3 interfaces use a default
adjacency for the interface & address family from the corresponding
interface pair. However, there are entries in the linux-cp adj table
that are created for them. Managing these entries might cause a
segfault because the rewrite data might exceed the reserved space for
it of 28 bytes in the linux-cp adj key (e.g. in case of GRE IPv6).

With this change, stop creating adjacencies for tun/L3 interfaces in
the linux-cp adj table and delegating them.

Signed-off-by: Alexander Chernavin <achernavin@netgate.com>
Change-Id: I4bcd685860053ab87c65064c182e3ed53fd4fae9