We'll be moving to a model wherein dst_entry route objects do not
have a precomputed neighbour entry attached to them, instead they
are looked up efficiently on an as-needed basis.

Most of the covnersions consist of simply using dst_neigh_lookup() to
find the neigh (using dst_entry and IPV4/IPV6 destination address as
the necessary arguments) and then explicitly releasing the neigh entry
once we are with it.

I intend to toss these into net-next, thanks.