Fix module load errors for test_ari_model.so.

You cannot use a function pointer variable with an external function from
another dynamically loaded module because data variables are always
resolved even with RTLD_LAZY.

* Added wrapper functions for ast_ari_validate_int() and
ast_ari_validate_string() to use instead for the function pointer
variable.

(closes issue ASTERISK-22457)
Reported by: David M. Lee
........

Merged revisions 399207 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@399208 f38db490-d61c-443f-a65b-d21fe96a405b