multimedia/openh264: update to 1.6.0

API/ABI has changed, so bump PORTREVISION in consumers. Some of those
are marked BROKEN that may need a fix similar to libav.

https://git.libav.org/?p=libav.git;a=commitdiff;h=d825b1a53065

Changes: https://github.com/cisco/openh264/releases/tag/v1.6.0