[network] Make use of T3113 for paging

Add it to the configuration files and make use
of it in the the paging.c.
diff --git a/openbsc/src/openbsc.cfg.nanobts b/openbsc/src/openbsc.cfg.nanobts
index 7f98468..a1ceaec 100644
--- a/openbsc/src/openbsc.cfg.nanobts
+++ b/openbsc/src/openbsc.cfg.nanobts
@@ -12,6 +12,7 @@
  short name OpenBSC
  long name OpenBSC
  timer t3101 10
+ timer t3113 60
  bts 0
   type nanobts
   ip.access unit_id 1801 0