657835: IPv6 tests fail instead of being skipped

Detect ipv6 before testing ipv6 transports.

diff -up net-snmp-5.7.2.pre2/testing/fulltests/transports/T320udpv6_simple.rhel net-snmp-5.7.2.pre2/testing/fulltests/transports/T320udpv6_simple
--- net-snmp-5.7.2.pre2/testing/fulltests/transports/T320udpv6_simple.rhel	2012-07-12 04:23:25.000000000 +0200
+++ net-snmp-5.7.2.pre2/testing/fulltests/transports/T320udpv6_simple	2012-07-31 11:10:22.668307328 +0200
@@ -6,6 +6,13 @@ HEADER UDP6 Transport
 
 SKIPIFNOT NETSNMP_TRANSPORT_UDPIPV6_DOMAIN
 
+# primitive detection of ipv6
+if test `uname -s` == "Linux" ; then
+    if test ! -e /proc/net/if_inet6; then
+        SKIP
+    fi
+fi
+
 #
 # Begin test
 #
diff -up net-snmp-5.7.2.pre2/testing/fulltests/transports/T330tcpv6_simple.rhel net-snmp-5.7.2.pre2/testing/fulltests/transports/T330tcpv6_simple
--- net-snmp-5.7.2.pre2/testing/fulltests/transports/T330tcpv6_simple.rhel	2012-07-12 04:23:25.000000000 +0200
+++ net-snmp-5.7.2.pre2/testing/fulltests/transports/T330tcpv6_simple	2012-07-31 11:10:07.756378344 +0200
@@ -6,6 +6,13 @@ HEADER TCP6 Transport
 
 SKIPIFNOT NETSNMP_TRANSPORT_TCPIPV6_DOMAIN
 
+# primitive detection of ipv6
+if test `uname -s` == "Linux" ; then
+    if test ! -e /proc/net/if_inet6; then
+        SKIP
+    fi
+fi
+
 #
 # Begin test
 #