migration: Fix block migration flag case

Fix the case where when a migration with a bad protocol is tried,
we leave the block migration capability set.

(This is a cut down version of my 'migration: Fix block failure cases'
where it's other case was fixed by Peter's dd0ee30c )

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20180316202114.32345-1-dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/migration.c

@@ -1428,6 +1428,7 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
                    "a valid migration protocol");
         migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                           MIGRATION_STATUS_FAILED);
+        block_cleanup_parameters(s);
         return;
     }