Updated RPL default memory sof and hard limit to 2/4 from 1/2.

This is mandatory change to support store 16 version update.

Change-Id: Id7111a323580bafc34693f9b52ce455feb83517b

Author: Juha Heiskanen

source/RPL/rpl_control.c

@@ -60,8 +60,8 @@
 const uint8_t ADDR_LINK_LOCAL_ALL_RPL_NODES[16] = { 0xff, 0x02, [15] = 0x1a };
 
 /* Sensible default limits for a 6LoWPAN-ND node */
-static size_t rpl_purge_threshold = 1 * 1024;
-static size_t rpl_alloc_limit = 2 * 1024; // 0 means no limit
+static size_t rpl_purge_threshold = 2 * 1024;
+static size_t rpl_alloc_limit = 4 * 1024; // 0 means no limit
 
 static size_t rpl_alloc_total;
 #define RPL_ALLOC_OVERHEAD 8