gbproxy: convert bss_nses from llist_head to hashtable

For the common lookup-by-nsei, this should reduce the computational
complexity significantly.

Depends: libosmocore.git I8ef73a62fe9846ce45058eb21cf999dd3eed5741
Change-Id: Idbb6a362332bb6e3ce22102e7409ae80d0980f44
diff --git a/TODO-RELEASE b/TODO-RELEASE
index 6b29a87..1e409b5 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -1,2 +1,3 @@
 #component	what		description / commit summary line
 manual				needs common chapter cs7-config.adoc, vty_cpu_sched.adoc from osmo-gsm-manuals > 0.3.0
+configure.ac	libosmocore	depend on next released libosmocore after 1.4.x with hashtable support