net/*: Fix FSF address in file headers

net/*: 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: John Fastabend <[email protected]>
CC: Alex Duyck <[email protected]>
CC: Marcel Holtmann <[email protected]>
CC: Gustavo Padovan <[email protected]>
CC: Johan Hedberg <[email protected]>
CC: Jamal Hadi Salim <[email protected]>
Signed-off-by: Jeff Kirsher <[email protected]>
Signed-off-by: David S. Miller <[email protected]>