Adjust iface_khandler_deregister() definition to avoid clang 15 warning
With clang 15, the following -Werror warning is produced:
sys/netpfil/ipfw/ip_fw_iface.c:159:26: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes] iface_khandler_deregister() ^ void
This is because iface_khandler_deregister() is declared with a (void)
argument list, but defined with an empty argument list. Make the
definition match the declaration.
MFC after: 3 days
(cherry picked from commit 4100dc46c78cef408369c0fc8dcfd1f87783a1ca)