mdns: fix possible race condition when checking DHCP status on WIFI_EVENT_STA_CONNECT...

mdns: fix possible race condition when checking DHCP status on WIFI_EVENT_STA_CONNECTED event.

tcpip_adapter_dhcpc_get_status() returns the actual internal value of dhcp client without any locking or TCP/IP stack context call, so when CONNECTED event fired with default settings it started DHCP client in TCP/IP stack context and at the same time mdns event handler checking actual DHCP state, which could still be INIT (not STARTED). Purpose of this check is to enable PCB if DHCP was stopped before setting network interface up (typically static IP settings), so the solutin is to check against TCPIP_ADAPTER_DHCP_STOPPED state