lib:ldb-samba: Improve calculate_popt_array_length()

lib:ldb-samba: Improve calculate_popt_array_length()

Note that memcmp() doesn't work well with padding bytes. So avoid it!

(gdb) ptype/o struct poptOption
/* offset    |  size */  type = struct poptOption {
/*    0      |     8 */    const char *longName;
/*    8      |     1 */    char shortName;
/* XXX  3-byte hole  */
/*   12      |     4 */    unsigned int argInfo;
/*   16      |     8 */    void *arg;
/*   24      |     4 */    int val;
/* XXX  4-byte hole  */
/*   32      |     8 */    const char *descrip;
/*   40      |     8 */    const char *argDescrip;

                           /* total size (bytes):   48 */

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
(cherry picked from commit c2c7c1f50a8acb3169e19ba4329aa78839b66def)