linuxlist.h: add llist_first/last_entry macros

Copy list_first_entry, list_first_entry_or_null and list_last_entry from
current linux kernel's tools/include/linux/list.h and rename to llist_*.
Slightly adjust API doc but stay as close to the source as possible.

This can replace similar implementations in osmo-bts-octphy's l1_if.c,
in openbsc's gtphub.c and in osmo-hlr's gsup_server.c.

Change-Id: I4eac5be0c0b2cede04464c4c3a0873102d952453
1 file changed