config+lsdb: Retry retrieve each LSA for `lsa-refresh-time`

This commit also includes extension of the config file
(`lsa-interest-lifetime` parameter in general section)

Change-Id: Ifd01af8cc98d41f7bdc953799a280e4b4269a358
Refs: #1873, #1874
diff --git a/nlsr.conf b/nlsr.conf
index 8b10210..48f34a6 100644
--- a/nlsr.conf
+++ b/nlsr.conf
@@ -9,9 +9,11 @@
   router /%C1.Router/cs/pollux    ; name of the router in ndn URI format
 
   ; lsa-refresh-time is the time in seconds, after which router will refresh its LSAs
-
   lsa-refresh-time 1800      ; default value 1800. Valid values 240-7200
 
+  ; InterestLifetime (in seconds) for LSA fetching
+  lsa-interest-lifetime 4    ; default value 4. Valid values 1-60
+
   ; log-level is to set the levels of log for NLSR
 
   log-level  INFO       ; default value INFO, valid value DEBUG, INFO