smb3: fix incorrect session setup check for multiuser mounts

A recent change to how the SMB3 server (socket) and session status
is managed regressed multiuser mounts by changing the check
for whether session setup is needed to the socket (TCP_Server_info)
structure instead of the session struct (cifs_ses). Add additional
check in cifs_setup_sesion to fix this.

Fixes: 73f9bfbe

 ("cifs: maintain a state machine for tcp/smb/tcon sessions")
Reported-by: Ronnie Sahlberg <lsahlber@redhat.com>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>