1) Fix up locking in nfs_up() and nfs_down.

1) Fix up locking in nfs_up() and nfs_down.
2) Reduce the acquisitions of the Giant lock in the nfs_socket.c paths significantly.
- We don't need to acquire Giant before tsleeping on lbolt anymore,
  since jhb specialcased lbolt handling in msleep.
- nfs_up() needs to acquire Giant only if printing the "server up"
  message.
- nfs_timer() held Giant for the duration of the NFS timer processing,
  just because the printing of the message in nfs_down() needed it
  (and we acquire other locks in nfs_timer()). The acquisition of
  Giant is moved down into nfs_down() now, reducing the time Giant is
  held in that path.

Reported by: Kris Kennaway