dlz_ldap_driver.c: error: this statement may fall through

Build configured with --with-dlz-ldap produces the following error/warning:

../../contrib/dlz/drivers/dlz_ldap_driver.c: In function ‘dlz_ldap_create’:
../../contrib/dlz/drivers/dlz_ldap_driver.c:957:20: error: this statement may fall through [-Werror=implicit-fallthrough=]
  957 |                 if (result != ISC_R_SUCCESS) {
      |                    ^
../../contrib/dlz/drivers/dlz_ldap_driver.c:960:9: note: here
  960 |         case 11:
      |         ^~~~
../../contrib/dlz/drivers/dlz_ldap_driver.c:962:20: error: this statement may fall through [-Werror=implicit-fallthrough=]
  962 |                 if (result != ISC_R_SUCCESS) {
      |                    ^
../../contrib/dlz/drivers/dlz_ldap_driver.c:965:9: note: here
  965 |         case 10:
      |         ^~~~
../../contrib/dlz/drivers/dlz_ldap_driver.c:966:20: error: this statement may fall through [-Werror=implicit-fallthrough=]
  966 |                 if (strlen(argv[9]) > 0) {
      |                    ^
../../contrib/dlz/drivers/dlz_ldap_driver.c:972:9: note: here
  972 |         case 9:
      |         ^~~~

Required for #3310 (closed).