SMB3: Fix length checking of SMB3.11 negotiate request

SMB3: Fix length checking of SMB3.11 negotiate request

The length checking for SMB3.11 negotiate request includes
"negotiate contexts" which caused a buffer validation problem
and a confusing warning message on SMB3.11 mount e.g.:

     SMB2 server sent bad RFC1001 len 236 not 170

Fix the length checking for SMB3.11 negotiate to account for
the new negotiate context so that we don't log a warning on
SMB3.11 mount by default but do log warnings if lengths returned
by the server are incorrect.

CC: Stable <[email protected]>
Signed-off-by: Steve French <[email protected]>
Reviewed-by: Aurelien Aptel <[email protected]>
Reviewed-by: Pavel Shilovsky <[email protected]>