SUNRPC: use different lock keys for INET6 and LOCAL

xprtsock.c reclassifies sock locks based on the protocol.
However there are 3 protocols and only 2 classification keys.
The same key is used for both INET6 and LOCAL.

This causes lockdep complaints.  The complaints started since Commit
ea9afca8 ("SUNRPC: Replace use of socket sk_callback_lock with
sock_lock") which resulted in the sock locks beings used more.

So add another key, and renumber them slightly.

Fixes: ea9afca8 ("SUNRPC: Replace use of socket sk_callback_lock with sock_lock")
Fixes: 176e21ee

 ("SUNRPC: Support for RPC over AF_LOCAL transports")
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>