gst1-plugins-bad: Add bug URL for the opencv modules issue

A bug has been reported upstream to fix this issue properly, and a
GStreamer developer agreed with our proposal. We add the bug URL to
comments on Config.in to let the interested users follow the progress of
this issue.

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>