Reduce the default kf_max_dist to 128.

Reduce the default kf_max_dist to 128.

The default maximum keyframe interval is 9999, or over five minutes
at normal video rates. When the encoder produces streams with such
a long interval seeking (with correct output) is more expensive,
and live streaming is impossible.

Of course the encoding application should set this parameter
based on its knowledge of the intended use of the stream, but
reducing the default gives better results for applications
which do not.

Change-Id: I900b15d74ce72ecc3ade4d43f758c5cf97a2098a