CIFS: Respect reconnect in non-MTU credits calculations

Every time after a session reconnect we don't need to account for
credits obtained in previous sessions. Make use of the recently
added cifs_credits structure to properly calculate credits for
non-MTU requests the same way we did for MTU ones.

Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>