linuxlist.h: add llist_count()

After subchan_demux.c in libosmo-abis, osmo-bts/common/vty.c and openbsc's
gtphub_test.c, more places would like to count the llist items (mostly unit
tests). Instead of proliferating numerous local implementations, add here.

NOTE: other than the previous llist_len() implementations, this one returns an
*unsigned* length, which might need some adjusting of current callers.

Call this llist_count() rather than llist_len() to highlight the fact that this
is actively iterating. This also avoids a potential naming conflict when
library versions mismatch.

Change-Id: Ic49adc7a346f5722bf624d7d3b4a735e4220ae15
1 file changed