NFSv4/v4.1: Verify the client owner id during trunking detection

While we normally expect the NFSv4 client to always send the same client
owner to all servers, there are a couple of situations where that is not
the case:
 1) In NFSv4.0, switching between use of '-omigration' and not will cause
    the kernel to switch between using the non-uniform and uniform client
    strings.
 2) In NFSv4.1, or NFSv4.0 when using uniform client strings, if the
    uniquifier string is suddenly changed.

This patch will catch those situations by checking the client owner id
in the trunking detection code, and will do the right thing if it notices
that the strings differ.

Cc: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>