[Hardy] SRU: SUNRPC: Fix autobind on cloned rpc clients

[Stefan Bader]

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/212485
Bug: #212485, #341783

SRU justification:

Impact: Having NFS mounted filesystems with autobinding in use there seems
to be a good chance that cloned clients might call rpcb_getport_async()
and thus trigger a Bug() statement in the code.

Fix: A cherry pick from upstream to walk to the parent client to find out
who "owns" the port. Fix was verified to be working.

Testcase: (from the report)
- desktop system mounts /home/ with nfs4
- login with gdm, start firefox and do some browsing, by entering some
  urls in the location bar
- issue some find /home & commands
- unplug the network cable