net: say "local" instead of "static" addresses in ndo_dflt_fdb_{add,del}

"Static" is a loaded word, and probably not what the author meant when
the code was written.

In particular, this looks weird:
$ bridge fdb add dev swp0 00:01:02:03:04:05 local        # totally fine, but
$ bridge fdb add dev swp0 00:01:02:03:04:05 static
[ 2020.708298] swp0: FDB only supports static addresses  # hmm what?

By looking at the implementation which uses dev_uc_add/dev_uc_del it is
absolutely clear that only local addresses are supported, and the proper
Network Unreachability Detection state is being used for this purpose
(user space indeed sets NUD_PERMANENT when local addresses are meant).
So it is just the message that is wrong, fix it.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>