addr: Reset unused portion of binary address in nl_addr_set_binary_addr()

memset() the binary address before overwriting it with new data
to avoid leaving around old portions of the address.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
addr: improve API reference documentation for nl_addr_*()

Signed-off-by: Thomas Graf <tgraf@suug.ch>
addr: Update to latest address familiy definition for translation

Signed-off-by: Thomas Graf <tgraf@suug.ch>
tests: Add check based unit test system

Introduces new unit tests based on `check`. Each subsystem/module can
have its own unit tests in tests/check-<name>.c that will be linked
together in tests/check-all.c.

Running 'make check' will compile and run the unit tests automatically.

A reference unit test implementation has been done for the abstract
address module.

Signed-off-by: Thomas Graf <tgraf@suug.ch>