auto-t: use tmp radvd pid file

On some systems the default radvd pid file location is not accessible.
Specify it to be under /tmp instead.

While there, enable full radvd debug output so it is logged when
test-runner is invoked with the --log option.

autotests/testNetconfig/connection_test.py

@@ -87,7 +87,7 @@ class Test(unittest.TestCase):
         config = open('/tmp/radvd.conf', 'w')
         config.write('interface ' + hapd.ifname + ' { AdvSendAdvert on; AdvManagedFlag on; };')
         config.close()
-        cls.radvd_pid = ctx.start_process(['radvd', '-n', '-C', '/tmp/radvd.conf'])
+        cls.radvd_pid = ctx.start_process(['radvd', '-n', '-d5', '-p', '/tmp/radvd.pid', '-C', '/tmp/radvd.conf'])
 
     @classmethod
     def tearDownClass(cls):