nl_addr_parse handling of 'default', 'any', and 'all'

nl_addr_parse handling of 'default', 'any', and 'all'

I found a small bug in the nl_addr_parse function when being passed the
strings "default", "any", or "all".  Currently nl_addr_parse will create
a zeroed nl_addr with a length corresponding to the family/hint or
AF_INET if omitted.  This behavior when used in conjunction with the
libnl-route library to add default routes to the system has the side
effect of creating a route to the host address 0.0.0.0/32.

Attached is a patch that matches the iproute2 behavior more closely
where we do set the family but the length of the nl_addr is set to 0.