6lowpan: Remove __init tag from lowpan_netlink_fini().

commit a07fdcec upstream.

It's called from both __init and __exit code, so neither
tag is appropriate.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>