Changes

ggsn: osmo-ggsn.src.cfg: tweak log output

* Print log levels.
* Don't print categories as hex.
* Print the basename at the end of the line.
* Remove "logging level lgtp debug", there already is
  "logging level lgtp info" further above, and this is a more sensible
  setting. With "debug" there are way too many log messages in e.g.
  TC_lots_of_concurrent_pdp_ctx.

Change-Id: I771d07645ea6da91f2c93f0954d99a37c866629a