NET, and never mapped IPv4 AF_INET6 addresses.  Both
nfs_match_client() and nfs_find_client() can now share the same
address comparison logic, so fold them together.

We can also dispense with of most of the conditional compilation
in here.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
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