Remove unstable_test decorator

Removes unstable_test decorator from
test_server_connectivity_cold_migration_revert test
since the related bug seems to be gone and the test
passes in most of the jobs.

Closes-Bug: 1836595
Change-Id: Ifc691971c71d89615d0e789cf6df884d2224047d
diff --git a/tempest/scenario/test_network_advanced_server_ops.py b/tempest/scenario/test_network_advanced_server_ops.py
index 1c00212..e630e29 100644
--- a/tempest/scenario/test_network_advanced_server_ops.py
+++ b/tempest/scenario/test_network_advanced_server_ops.py
@@ -283,7 +283,6 @@
         self._wait_server_status_and_check_network_connectivity(
             server, keypair, floating_ip)
 
-    @decorators.unstable_test(bug='1836595')
     @decorators.idempotent_id('25b188d7-0183-4b1e-a11d-15840c8e2fd6')
     @testtools.skipUnless(CONF.compute_feature_enabled.cold_migration,
                           'Cold migration is not available.')