Fix test/msan/ifaddrs.cc for NetBSD

Summary:
NetBSD requires to include <sys/socket.h> for struct sockaddr.

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, eugenis, vitalybuka

Reviewed By: vitalybuka

Subscribers: llvm-commits, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D41015

llvm-svn: 320223