Protocols like mdns requires IPv6 link local address to be advertised in its
records (AAAA record). LWIP::Interface::bringup() API is creating IPv6 link
local address;But as of now there is no API exposed by mbed-os to get the
IPv6 link local address.
This new API is required to deliver mDNS library support on mbed-os for Cypress
platforms. Unit tested it by invoking get_ipv6_link_local_address with a simple
application.
Allow more than one callback to be register to NetworkInterfaces.
This introduces new APIs:
void NetworkInterface::add_event_listener(...);
void NetworkInterface::remove_event_listener(...);
Which internally calls interfaces attach() functions.
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.