cifs: prevent data race in cifs_reconnect_tcon()

cifs: prevent data race in cifs_reconnect_tcon()

[ Upstream commit 1bcd548d935a33c6fc58331405eb1b82fd6150de ]

Make sure to get an up-to-date TCP_Server_Info::nr_targets value prior
to waiting the server to be reconnected in cifs_reconnect_tcon().  It
is set in cifs_tcp_ses_needs_reconnect() and protected by
TCP_Server_Info::srv_lock.

Create a new cifs_wait_for_server_reconnect() helper that can be used
by both SMB2+ and CIFS reconnect code.

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Stable-dep-of: bc962159e8e3 ("cifs: avoid race conditions with parallel reconnects")
Signed-off-by: Sasha Levin <sashal@kernel.org>