Fix log level "everything" and make it equal to "debug"

As Holger points out "logging level XXX everything" wasn't working, as
it sets category->loglevel to 0, which is checked in osmo_vlogp() and
will never get logged.
Add UMTS RRC message types
Added a ring buffer log target to store the last N log messages.

The log target can be used via log alarms and show alarms.
Why? This feature was proposed/requested at
http://openbsc.osmocom.org/trac/wiki/Tasks/ErrorLogTarget
All messages use the same amount of space, prioritizing simplicity.
Revert "Added a ring buffer log target to store the last N log messages."

I noticed some more issues and it is the easiest to revert and include
the fixed version.

This reverts commit 73377229bb33ab79682ce4b126a63602d13304ad.
Added a ring buffer log target to store the last N log messages.

The log target can be used via log alarms and show alarms.
Why? This feature was proposed/requested at
http://openbsc.osmocom.org/trac/wiki/Tasks/ErrorLogTarget
All messages use the same amount of space, prioritizing simplicity.
Follow up fix for the log level "everything"

Commit cd6ed82d1ff48f47ad9e33e6322df62896a76ed5 made "EVERYTHING"
map to LOGL_DEBUG but when writing out the configuration the following
would be written:

  logging level all unknown 0x0

This happend because no string was found for the value 0. Address it
by adding a legacy check for 0 and write out the str from the index
0. Currently this is "EVERYTHING".