srsepc.conf.tmpl: double value of T3413 (paging timer)

we've already incrased the t3413 value in 9c7fd618d226dc532b9408c329cfc2380de4850a
but realized it may still be too low in some cases.

we set it to 12s now.

Change-Id: I9c3c59c0ff8f539a44b420f8ba31eea016c211ce
diff --git a/src/osmo_gsm_tester/templates/srsepc.conf.tmpl b/src/osmo_gsm_tester/templates/srsepc.conf.tmpl
index 62f9977..d6ecaec 100644
--- a/src/osmo_gsm_tester/templates/srsepc.conf.tmpl
+++ b/src/osmo_gsm_tester/templates/srsepc.conf.tmpl
@@ -31,7 +31,7 @@
 dns_addr = 8.8.8.8
 encryption_algo = EEA0
 integrity_algo = EIA1
-paging_timer = 6
+paging_timer = 12
 
 #####################################################################
 # HSS configuration