[msan] Replace AF_INET with AF_UNIX to avoid IPv4 vs IPv6 issues.

Summary: This reverts commit 79cf16bf224d6ac9fb9e0356c5947ebc4fd6ff92.

Reviewers: eugenis

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31895

llvm-svn: 299860