netfilter: Fix FSF address in file headers

Several files refer to an old address for the Free Software Foundation
in the file header comment.  Resolve by replacing the address with
the URL <http://www.gnu.org/licenses/> so that we do not have to keep
updating the header comments anytime the address changes.

CC: netfilter@vger.kernel.org
CC: Pablo Neira Ayuso <pablo@netfilter.org>
CC: Patrick McHardy <kaber@trash.net>
CC: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>