Add new interceptors: getnetent(3) family

Summary:
getnetent, getnetbyaddr, getnetbyname - get network entry

Reuse them on NetBSD.

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, vitalybuka

Reviewed By: vitalybuka

Subscribers: llvm-commits, kubamracek, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D43543

llvm-svn: 326163