dlm: use sock_create_lite inside tcp_accept_from_sock

With commit 0ffdaf5b ("net/sock: add WARN_ON(parent->sk)
in sock_graft()"), a calltrace happened as follows:

[  457.018340] WARNING: CPU: 0 PID: 15623 at ./include/net/sock.h:1703 inet_accept+0x135/0x140
...
[  457.018381] RIP: 0010:inet_accept+0x135/0x140
[  457.018381] RSP: 0018:ffffc90001727d18 EFLAGS: 00010286
[  457.018383] RAX: 0000000000000001 RBX: ffff880012413000 RCX: 0000000000000001
[  457.018384] RDX: 000000000000018a RSI: 00000000fffffe01 RDI: ffffffff8156fae8
[  457.018384] RBP: ffffc90001727d38 R08: 0000000000000000 R09: 0000000000004305
[  457.018385] R10: 0000000000000001 R11: 0000000000004304 R12: ffff880035ae7a00
[  457.018386] R13: ffff88001282af10 R14: ffff880034e4e200 R15: 0000000000000000
[  457.018387] FS:  0000000000000000(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000
[  457.018388] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  457.018389] CR2: 00007fdec22f9000 CR3: 0000000002b5a000 CR4: 00000000000006f0
[  457.018395] Call Trace:
[  457.018402]  tcp_accept_from_sock.part.8+0x12d/0x449 [dlm]
[  457.018405]  ? vprintk_emit+0x248/0x2d0
[  457.018409]  tcp_accept_from_sock+0x3f/0x50 [dlm]
[  457.018413]  process_recv_sockets+0x3b/0x50 [dlm]
[  457.018415]  process_one_work+0x138/0x370
[  457.018417]  worker_thread+0x4d/0x3b0
[  457.018419]  kthread+0x109/0x140
[  457.018421]  ? rescuer_thread+0x320/0x320
[  457.018422]  ? kthread_park+0x60/0x60
[  457.018424]  ret_from_fork+0x25/0x30

Since newsocket created by sock_create_kern sets it's
sock by the path:

	sock_create_kern -> __sock_creat
			 ->pf->create => inet_create
			 -> sock_init_data

Then WARN_ON is triggered by "con->sock->ops->accept =>
inet_accept -> sock_graft", it also means newsock->sk
is leaked since sock_graft will replace it with a new
sk.

To resolve the issue, we need to use sock_create_lite
instead of sock_create_kern, like commit 0933a578
("rds: tcp: use sock_create_lite() to create the accept
socket") did.

Reported-by: Zhilong Liu <zlliu@suse.com>
Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: David Teigland <teigland@redhat.com>