cifs: throw a warning if negotiate or sess_setup ops are passed NULL server or sessio...

These look pretty cargo-culty to me, but let's be certain. Leave
them in place for now. Pop a WARN if it ever does happen. Also,
move to a more standard idiom for setting the "server" pointer.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>

diff --cc fs/cifs/cifssmb.c
Simple merge

diff --cc fs/cifs/sess.c
Simple merge

diff --cc fs/cifs/smb2pdu.c
Simple merge