Sync mbed_lib.json with Mbed OS (#1935)

Sync mbed_lib.json with the Mbed OS commits:
-585a4b6 Add nanostack support for KW41Z
-9a0fc98 Hotfix for PR #7778
-1ef0479 On KW24D and NCS36510 default to smaller Nanostack configuration
-f0bf771 Get rid of FEATURE_NANOSTACK

Author: Arto Kinnunen

mbed_lib.json

@@ -1,7 +1,24 @@
 {
     "name": "nanostack",
     "config": {
-        "configuration": "nanostack_full"
+        "configuration": {
+            "help": "Build time configuration. Refer to Handbook for valid values. Default: full stack",
+            "value": "nanostack_full"
+        }
     },
-    "macros": ["NS_USE_EXTERNAL_MBED_TLS"]
+    "macros": ["NS_USE_EXTERNAL_MBED_TLS"],
+    "target_overrides": {
+        "KW24D": {
+            "nanostack.configuration": "lowpan_router"
+        },
+        "NCS36510": {
+            "nanostack.configuration": "lowpan_router"
+        },
+        "TB_SENSE_12": {
+            "nanostack.configuration": "lowpan_router"
+        },
+        "KW41Z": {
+            "nanostack.configuration": "lowpan_router"
+        }
+    }
 }