Fix printf formats
Initial msp library implementation with connection state tracking
Improve msp failure handling
Pipe file contents across msp connection
Test connection keep alive and timeouts
Refactor interface addresses to use new socket_address struct
Allow interfaces to use local unix addresses

- broadcast packets are sent to all sockets in the same folder
- switched most tests to use local sockets
Ensure only interfaces that are UP are closed
Generalise method for defining multiple interfaces
Improve tests
Reduce spam of link state packets