Merge pull request #9471 from mtomczykmobica/ONME-3868

lwipstack: mem-size set to the to minimal working size with DTLS

Author: Cruz Monrreal

features/lwipstack/mbed_lib.json

@@ -130,10 +130,10 @@
             "pbuf-pool-size" :  10
         },
         "STM": {
-            "mem-size": 25600
+            "mem-size": 2310
         },
         "Freescale": {
-            "mem-size": 16384
+            "mem-size": 33270
         },
         "LPC1768": {
             "mem-size": 16362