CIFS: Simplify connection structure search calls

Use separate functions for comparison between existing structure
and what we are requesting for to make server, session and tcon
search code easier to use on next superblock match call.

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