Added Multihoming feature to LWIP (ability to use more than one network interfaces) for increasing networking reliability.
This involves:
LWIP interface
LWIP IP routing
DNS storage
Sockets (bind to interface name possibility)
possibility to add non default network interface
cellular middleware modifications if cellular connection is used
This is slight API change, as a new return code is introduced.
Intention is to properly support asyncronous drivers that might
not be able to get new operation into execution, therefore they
need to return BUSY.