smb: client: change lease epoch type from unsigned int to __u16

MS-SMB2 section 2.2.13.2.10 specifies that 'epoch' should be a 16-bit
unsigned integer used to track lease state changes. Change the data
type of all instances of 'epoch' from unsigned int to __u16. This
simplifies the epoch change comparisons and makes the code more
compliant with the protocol spec.

Cc: stable@vger.kernel.org
Signed-off-by: Meetakshi Setiya <msetiya@microsoft.com>
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>