MFstable/10 r294300:

MFC r293715:

Fix a mismerge from NetBSD in r162194 with xdr_rpcb_entry_list_ptr(..)

This fixes the potential NULL pointer dereference properly, and also fixes
memory leaks encountered in the process of iterating through *rp.

Found by: Valgrind
Submitted by: Miles Ohlrich <miles.ohlrich@isilon.com>