Fix IPv6 default masks for SLAAC

IETF doesn't recommend use of IPv6 networks
with masks not "/64". Recommended subnetting is
3-1-4 - 48 for provider, 16 for subnetting and
64 for network. For example SLAAC will not
work if you use subnets different from /64.
Test with port update will not work until
bug 1364166 is fixed, added attribute to it.

Change-Id: I260c820dbde1f98b569e564c7b5e7e558e431c0d
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 29f80bd..dcc3c18 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -747,10 +747,10 @@
 
 # The cidr block to allocate tenant ipv6 subnets from (string
 # value)
-#tenant_network_v6_cidr=2003::/64
+#tenant_network_v6_cidr=2003::/48
 
 # The mask bits for tenant ipv6 subnets (integer value)
-#tenant_network_v6_mask_bits=96
+#tenant_network_v6_mask_bits=64
 
 # Whether tenant network connectivity should be evaluated
 # directly (boolean value)