Added solaris IPv6 checking to configure. Fixes #6438.

Patch from Tim Spriggs.

configure.in

@@ -196,7 +196,7 @@ AC_ARG_ENABLE(ipv6,
 		[don't even try to use IPv6]))
 if test x"$enable_ipv6" != x"no"; then
 	AC_MSG_CHECKING([ipv6 stack type])
-	for i in inria kame linux-glibc linux-inet6 toshiba v6d zeta; do
+	for i in inria kame linux-glibc linux-inet6 solaris toshiba v6d zeta; do
 		case $i in
 		inria)
 			# http://www.kame.net/
@@ -240,6 +240,16 @@ AC_DEFINE(INET6, 1, [true if you have IPv6])])
 				CFLAGS="-I/usr/inet6/include $CFLAGS"
 			fi
 			;;
+		solaris)
+			# http://www.sun.com
+			AC_EGREP_CPP(yes, [
+#include <netinet/ip6.h>
+#ifdef __sun
+yes
+#endif],
+				[ipv6type=$i;
+				AC_DEFINE(INET6, 1, [true if you have IPv6])])
+			;;
 		toshiba)
 			AC_EGREP_CPP(yes, [
 #include <sys/param.h>