Adjust ipfw_iface_{init,destroy}() definitions to avoid clang 15 warning
With clang 15, the following -Werror warnings are produced:
sys/netpfil/ipfw/ip_fw_iface.c:206:16: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes] ipfw_iface_init() ^ void sys/netpfil/ipfw/ip_fw_iface.c:219:19: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes] ipfw_iface_destroy() ^ void
This is because ipfw_iface_init() and ipfw_iface_destroy() are declared
with (void) argument lists, but defined with empty argument lists. Make
the definitions match the declarations.
MFC after: 3 days