appletalk: remove the BKL

This changes appletalk to use lock_sock instead of
lock_kernel for serialization. I tried to make sure
that we don't hold the socket lock during sleeping
functions, but I did not try to prove whether the
locks are necessary in the first place.

Compile-tested only.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: David Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org