cifs: fix SMB2 signing enablement in cifs_enable_signing

Commit 9ddec561 (cifs: move handling of signed connections into
separate function) broke signing on SMB2/3 connections. While the code
to enable signing on the connections was very similar between the two,
the bits that get set in the sec_mode are different.

Declare a couple of new smb_version_values fields and set them
appropriately for SMB1 and SMB2/3. Then change cifs_enable_signing to
use those instead.

Reported-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Tested-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Steve French <smfrench@gmail.com>