FreeSWITCH-FS-8767

Merge pull request #517 in FS/freeswitch from ~MBRANCA/freeswitch:bugfix/FS-8239-error-in-building-mod_av-on-centos to master

* commit 'fe1fa8c8fbf1785e8c3e5320b2c837feb4e14034':
  FS-8239 fix default value to avoid failed mod_av build on CentOS 7