MFstable/10 r304982:

MFstable/11 r304945:

MFC r304034:

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.

PR: 211790