dns: always set variable family in lookup()

Regression occurred that prevented the variable "family" from being set
properly when the lookup() function's "options" parameter was passed a
number instead of an object.

Also included a sanity check by setting the default value of "family" to
a value that will not pass verification.

Fixes: e643fe4 "dns: fix GetAddrInfo assert"
Reviewed-by: Alexis Campailla <alexis@janeasystems.com>
Reviewed-by: Trevor Norris <trev.norris@gmail.com>