Put NVMe/TCP sockets in their own class to avoid some lockdep warnings.
Sockets created by nvme-tcp are not exposed to user-space, and will not
trigger certain code paths that the general socket API exposes.

Lockdep complains about a circular dependency between the socket and
filesystem locks, because setsockopt can trigger a page fault with a
socket lock held, but nvme-tcp sends requests on the socket while file
system locks are held.

  ======================================================
  WARNING: possible circular locking dependency detected
  5.15.0-rc3 #1 Not tainted
  ------------------------------------------------------
  fio/1496 is trying to acquire lock:
  (sk_lock-AF_INET){+.+.}-{0:0}, at: tcp_sendpage+0x23/0x80

  but task is already holding lock:
  (&xfs_dir_ilock_class/5){+.+.}-{3:3}, at: xfs_ilock+0xcf/0x290 [xfs]

  which lock already depends on the new lock.

  other info that might help us debug this:

  chain exists of:
   sk_lock-AF_INET --> sb_internal --> &xfs_dir_ilock_class/5

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&xfs_dir_ilock_class/5);
                                lock(sb_internal);
                                lock(&xfs_dir_ilock_class/5);
   lock(sk_lock-AF_INET);

  *** DEADLOCK ***

  6 locks held by fio/1496:
   #0: (sb_writers#13){.+.+}-{0:0}, at: path_openat+0x9fc/0xa20
   #1: (&inode->i_sb->s_type->i_mutex_dir_key){++++}-{3:3}, at: path_openat+0x296/0xa20
   #2: (sb_internal){.+.+}-{0:0}, at: xfs_trans_alloc_icreate+0x41/0xd0 [xfs]
   #3: (&xfs_dir_ilock_class/5){+.+.}-{3:3}, at: xfs_ilock+0xcf/0x290 [xfs]
   #4: (hctx->srcu){....}-{0:0}, at: hctx_lock+0x51/0xd0
   #5: (&queue->send_mutex){+.+.}-{3:3}, at: nvme_tcp_queue_rq+0x33e/0x380 [nvme_tcp]

This annotation lets lockdep analyze nvme-tcp controlled sockets
independently of what the user-space sockets API does.

Link: https://lore.kernel.org/linux-nvme/CAHj4cs9MDYLJ+q+2_GXUK9HxFizv2pxUryUR0toX974M040z7g@mail.gmail.com/Signed-off-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>