Hi Vadim and Tom,
as LGPL v2.1-or-later is compatible with GPLv2-or-later, there is not really a strict requirement for license compatibiltiy reasons. Any application that links against the GPL-v2-or-later libosmocore has no license compatibility issues with LGPLv2-or-later, as GPLv2 is the stricter of the two licenses anyway.
Still, it is of course good if the entire library is covered under one license, and people don't have to research and follow different license terms for each file. Most importantly, we don't want people to assume all of the librray is LGPL, which is clearly not our intention.
Regards, Harald