net/fping: fix WITHOUT_IPV6 mode

If one builds and uses net/fping version 4.2 with option IPV6 disabled,
the command fping -4 always fails with wrong error message:

fping: can't specify both -4 and -6

This makes it impossible using fping probes with SmokePing
as it runs fping with -4 option. This change fixes this.
Also, do not install symlinks for fping6 and manual in this case.

PORTREVISION not bumped as default build is not affected.

PR:		238327
Approved by:	jharris@widomaker.com (maintainter timeout, 2 weeks)

net/fping/Makefile

@@ -24,10 +24,11 @@ CONFIGURE_ARGS=	--bindir="${PREFIX}/sbin" \
 		--enable-ipv4
 INSTALL_TARGET=	install-strip
 
-OPTIONS_DEFINE=IPV6
+OPTIONS_DEFINE=	IPV6
+OPTIONS_SUB=	yes
 IPV6_CONFIGURE_OFF=--disable-ipv6
 
-post-install:
+post-install-IPV6-on:
 	${RLN} ${STAGEDIR}${PREFIX}/sbin/fping  ${STAGEDIR}${PREFIX}/sbin/fping6
 	${RLN} ${STAGEDIR}${PREFIX}/man/man8/fping.8 ${STAGEDIR}${PREFIX}/man/man8/fping6.8
 

net/fping/files/patch-src_fping.c

@@ -0,0 +1,11 @@
+--- src/fping.c.orig	2019-02-19 20:54:45 UTC
++++ src/fping.c
+@@ -427,7 +427,7 @@ int main(int argc, char** argv)
+     while ((c = optparse_long(&optparse_state, longopts, NULL)) != EOF) {
+         switch (c) {
+         case '4':
+-            if (hints_ai_family != AF_UNSPEC) {
++            if (hints_ai_family == AF_INET6) {
+                 fprintf(stderr, "%s: can't specify both -4 and -6\n", prog);
+                 exit(1);
+             }

net/fping/pkg-plist

@@ -1,6 +1,6 @@
 @mode 4555
 sbin/fping
-sbin/fping6
+%%IPV6%%sbin/fping6
 @mode
 man/man8/fping.8.gz
-man/man8/fping6.8.gz
+%%IPV6%%man/man8/fping6.8.gz