fix issue: https://github.com/sonic-net/sonic-mgmt/issues/6479a (#13280)

What is the motivation for this PR?
Fix issue: #6479

How did you do it?
Replace duthost.hostname it with duthost.mgmt_ip

How did you verify/test it?
Run Test_syslog_source_ip

Any platform specific information?
Any

tests/syslog/test_syslog_source_ip.py

@@ -252,9 +252,9 @@ def configure_mgmt_vrf_test_data(self, localhost):
             logger.info("Create mgmt vrf")
             create_vrf(self.duthost, VRF_LIST[2])
             # when create mgmt vrf, dut connection will be lost for a while
-            localhost.wait_for(host=self.duthost.hostname, port=SONIC_SSH_PORT, search_regex=SONIC_SSH_REGEX,
+            localhost.wait_for(host=self.duthost.mgmt_ip, port=SONIC_SSH_PORT, search_regex=SONIC_SSH_REGEX,
                                state='absent', delay=1, timeout=30)
-            localhost.wait_for(host=self.duthost.hostname, port=SONIC_SSH_PORT, search_regex=SONIC_SSH_REGEX,
+            localhost.wait_for(host=self.duthost.mgmt_ip, port=SONIC_SSH_PORT, search_regex=SONIC_SSH_REGEX,
                                state='started', delay=2, timeout=180)
 
         for k, v in list(MGMT_IP_ADDRESSES.items()):