Some modules such as SCTP supplies a valid route entry as an input argument

Some modules such as SCTP supplies a valid route entry as an input argument
to ip_output(). The destionation is represented in a sockaddr{} object
that may contain other pieces of information, e.g., port number. This
same destination sockaddr{} object may be passed into L2 code, which
could be used to create a L2 entry. Since there exists a L2 table per
address family, the L2 lookup function can make address family specific
comparison instead of the generic bcmp() operation over the entire
sockaddr{} structure.

Note in the IPv6 case the sin6_scope_id is not compared because the
address is currently stored in the embedded form inside the kernel.
The in6_lltable_lookup() has to account for the scope-id if this
storage format were to change in the future.