NFS MP scaling changes.

• Eliminate the hideous nfs_sndlock that serialized NFS/TCP request senders thru the sndlock.
• Institute a new nfs_connectlock that serializes NFS/TCP reconnects. Add logic to wait for pending request senders to finish sending before reconnecting. Dial down the sb_timeo for NFS/TCP sockets to 1 sec.
• Break out the nfs xid manipulation under a new nfs xid lock, rather than over loading the nfs request lock for this purpose.
• Fix some of the locking in nfs_request.

Many thanks to Kris Kennaway for his help with this and for initiating the
MP scaling analysis and work. Kris also tested this patch thorougly.
Approved by: re@ (Ken Smith)