Changes

rate_ctr,CTRL[2/2]: log ctrg inst names invalid for CTRL

After the previous patch, magically all rate_ctr_groups in all osmo
programs will become accessible by their given rate_ctr_group_set_name()
IDs.

This also means that the strings passed to rate_ctr_group_set_name() now
are required to be a valid identifier, to not mix up the CTRL interface
syntax.

So far, only log an error, to figure out if we need mangling.

Related: OS#6545
Change-Id: Ic721219649e20960c7af5765ee4d3b641fef5081