Revert "Skip unstable v6 scenario tests"

This reverts commit 461c83d287311447854016a286d1bbaf9f822769.

The neutron L3 team has been doing testing for the past few weeks
with this test re-enabled and does not see the failures
associated with it any more.

Change-Id: Ie30e5443447c76a6c6bc8afdf8150d23ddb6857e
diff --git a/tempest/scenario/test_network_v6.py b/tempest/scenario/test_network_v6.py
index 364b6f5..59ebb7a 100644
--- a/tempest/scenario/test_network_v6.py
+++ b/tempest/scenario/test_network_v6.py
@@ -18,7 +18,6 @@
 
 from tempest import config
 from tempest.lib.common.utils import test_utils
-from tempest.lib import decorators
 from tempest.scenario import manager
 from tempest import test
 
@@ -255,7 +254,6 @@
         self._prepare_and_test(address6_mode='dhcpv6-stateless', n_subnets6=2,
                                dualnet=True)
 
-    @decorators.skip_because(bug="1540983")
     @test.idempotent_id('9178ad42-10e4-47e9-8987-e02b170cc5cd')
     @test.services('compute', 'network')
     def test_dualnet_multi_prefix_slaac(self):