lib: wrong #define used for IPV6_MINHOPCOUNT

The #define IPV6_MINHOPCNT define is never defined on any unix platform.
>From what I can tell the original implementation on the linux platform
was IPV6_MINHOPCNT, when it got accepted into the mainstream kernel
it was transformed into IPV6_MINHOPCOUNT.  Since we test for the
define before attempting to use the code it was silently doing nothing
for a long time.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/configure.ac b/configure.ac
index f68d86f..27014c3 100755
--- a/configure.ac
+++ b/configure.ac
@@ -1072,7 +1072,7 @@
 dnl IPv6 header checks
 dnl ------------------
 AC_CHECK_HEADERS([netinet6/in6.h netinet/in6_var.h netinet/icmp6.h \
-	netinet6/in6_var.h netinet6/nd6.h], [], [],
+	netinet6/in6_var.h netinet6/nd6.h linux/in6.h], [], [],
 	QUAGGA_INCLUDES)
 
 m4_define([QUAGGA_INCLUDES],dnl
@@ -1092,6 +1092,9 @@
 #if HAVE_NETINET6_ND6_H
 # include <netinet6/nd6.h>
 #endif
+#if HAVE_LINUX_IN6_H
+# include <linux/in6.h>
+#endif
 ])dnl
 
 dnl disable doc check
diff --git a/lib/sockunion.c b/lib/sockunion.c
index c7315f2..8f3540d 100644
--- a/lib/sockunion.c
+++ b/lib/sockunion.c
@@ -29,6 +29,10 @@
 #include "log.h"
 #include "jhash.h"
 
+#if defined(HAVE_LINUX_IN6_H)
+#include <linux/in6.h>
+#endif
+
 #ifndef HAVE_INET_ATON
 int
 inet_aton (const char *cp, struct in_addr *inaddr)
@@ -506,13 +510,13 @@
       return ret;
     }
 #endif /* IP_MINTTL */
-#ifdef IPV6_MINHOPCNT
+#ifdef IPV6_MINHOPCOUNT
   if (family == AF_INET6)
     {
-      int ret = setsockopt (sock, IPPROTO_IPV6, IPV6_MINHOPCNT, &minttl, sizeof(minttl));
+      int ret = setsockopt (sock, IPPROTO_IPV6, IPV6_MINHOPCOUNT, &minttl, sizeof(minttl));
       if (ret < 0)
 	  zlog (NULL, LOG_WARNING,
-		"can't set sockopt IPV6_MINHOPCNT to %d on socket %d: %s",
+		"can't set sockopt IPV6_MINHOPCOUNT to %d on socket %d: %s",
 		minttl, sock, safe_strerror (errno));
       return ret;
     }