attr: reject zero length addresses
attr: reject zero length addresses

A zero length address is not a valid address in netlink, so we should
not try to send them to the kernel.

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

thom311/libnl,thom311/libnl,thom311/libnl