Update GPL header in all source files to current recommended version

Update GPL header in all source files to current recommended version

This removes the postal address of the FSF and replaces
it with their URL.

Mostly generated with
sed -i -e 's@if not, write to the Free Software Foundation, Inc.,\
            @if not, see <https://www.gnu.org/licenses/>.@'
sed -i -e '/51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA/d'
sed -i -e '/59 Temple Place, Suite 330, Boston, MA  02111-1307  USA/d'

With some manual fix-ups afterwards.

Change-Id: Ic3959970fa9ab993e98d4b38c025fd0efc7b92f2
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20250803145126.23494-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg32481.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>