Similar to r293704, fix theoretical leak of netconfig(3) resources in
__rpcbind_is_up(..) if getnetconfig(3) is partly successful in allocating
resources, but not completely successful by moving the endnetconfig(3) call
up before we return from the function if nconf == NULL.

MFC after: 1 week
Reported by: Coverity
Submitted by: Miles Ohlrich <miles.ohlrich@isilon.com>
Sponsored by: EMC / Isilon Storage Division