ipv4: fib_rules: Dump FIB rules when registering FIB notifier

In commit c3852ef7 ("ipv4: fib: Replay events when registering FIB
notifier") we dumped the FIB tables and replayed the events to the
passed notification block.

However, we merely sent a RULE_ADD notification in case custom rules
were in use. As explained in previous patches, this approach won't work
anymore. Instead, we should notify the caller about all the FIB rules
and let it act accordingly.

Upon registration to the FIB notification chain, replay a RULE_ADD
notification for each programmed FIB rule, custom or not. The integrity
of the dump is ensured by the mechanism introduced in the above
mentioned commit.

Prevent regressions by making sure current listeners correctly sanitize
the notified rules.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>