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
New classes covered with unit tests: SocketAddress, EthernetInterface, EMACInterface, WiFiAccessPoint.
Also added missing namespace in front of mbed::Callback usages.
EMACInterface is covered by the EthernetInterface unit tests.
Rather than let "EthernetInterface" be the base EMAC NetworkInterface,
insert an "EMACInterface" class.
EthernetInterface then derives from EMACInterface and EthInterface.
A Wi-Fi driver can derive from EMACInterface and WiFiInterface - this
will be more logical than deriving from EthernetInterface and
WiFiInterface.
This does mean adding a couple of virtual inheritances to avoid
duplicate NetworkInterfaces:
NetworkInterface
/ \
virtual / \ virtual
/ \
EMACInterface WiFiInterface
\ /
\ /
\ /
MyCustomWiFiInterface