logging: fix missing description of global loglevel

OpenBSC> logging level
  all    Global setting for all subsystems <----- this description was missing
  rll    A-bis Radio Link Layer (RLL)
[...]

This problem was introduced by myself in:
"vty: integration with logging framework"
04139f14b6197e3ec996133a945af3fa8a68fb7a
1 file changed