net/libnfs: Import libnfs-6.0.2

LIBNFS is a client library for accessing NFS shares over a network.

LIBNFS offers three different APIs, for different use:
1, RAW: A fully async low level RPC library for NFS protocols
2, NFS ASYNC: A fully asynchronous library for high level vfs functions
3, NFS SYNC: A synchronous library for high level vfs functions