addr: allow constructing all-zero addresses
addr: allow constructing all-zero addresses

Allow easy contruction of all-zero addresses by not passing a buf to
copy. Since the object is allocated with calloc, the address data will
default to all-zero, and only the length needs to be set.

Signed-off-by: Jonas Gorski <9712c064bde5a52658fc87d6454b4956f9bf286b@bisdn.de>

thom311/libnl,thom311/libnl,thom311/libnl