Initialize ai to NULL and test for ai with type-appropriate values

Depending on the address family and ai_flags containing AI_V4MAPPED,
it might not do a proper DNS lookup on the provided DNS address

Convert some ai boolean true/false checks to NULL/non-NULL while here.

MFC after: 1 week
PR: 211790
Reported by: Herbie.Robinson@stratus.com
Sponsored by: EMC / Isilon Storage Division