Automate options INET/INET6 turning into MK_$opt_SUPPORT

correctly. Fixes if_gfe when building without INET6 and
simplifies if_gif's Makefile.

Sponsored by: Netflix, Inc

sys/conf/kern.opts.mk

@@ -79,6 +79,18 @@ MK_${var}:=	no
 .if defined(WITHOUT_${var}_SUPPORT) || ${MK_${var}} == "no"
 MK_${var}_SUPPORT:= no
 .else
+.if defined(KERNBUILDDIR)	# See if there's an opt_foo.h
+OPT_${var}!= cat ${KERNBUILDDIR}/opt_${var:tl}.h; echo
+.if ${OPT_${var}} == ""		# nothing -> no
+MK_${var}_SUPPORT:= no
+.else
 MK_${var}_SUPPORT:= yes
 .endif
+.else				# otherwise, yes
+MK_${var}_SUPPORT:= yes
+.endif
+.endif
 .endfor
+
+
+

sys/modules/if_gif/Makefile

@@ -8,13 +8,6 @@ SYSDIR?=${.CURDIR}/../..
 KMOD=	if_gif
 SRCS=	if_gif.c in_gif.c opt_inet.h opt_inet6.h
 
-.if defined(KERNBUILDDIR)
-OPT_INET6!= cat ${KERNBUILDDIR}/opt_inet6.h; echo
-.if empty(OPT_INET6)
-MK_INET6_SUPPORT=no
-.endif
-.endif
-
 .if ${MK_INET6_SUPPORT} != "no"
 SRCS+=	in6_gif.c
 .endif