tests: fix invalid hints flags dns test.

1 is actually a valid flag on SmartOS. More generally, hints flags'
values are defined by the underlying native flags, and these can have
different values on different systems.

Using (ADDRCONFIG | V4MAPPED) + 1 ensure that the flag will be invalid,
since it will always be different from ADDRCONFIG, V4MAPPED, ADDRCONFIG
| V4MAPPED,  0, 1 and any other combination of even flags.