Fix compilation warnings noticed in mbed-os (ARMmbed#1909)

Author: michalpasztamobica

source/6LoWPAN/Thread/thread_extension.h

@@ -85,7 +85,7 @@ uint8_t *thread_extension_discover_response_write(protocol_interface_info_entry_
 #define thread_extension_version_check(version) (false)
 #define thread_extension_discover_response_read(nwk_info, discover_response_tlv, data_ptr, data_len) ((void) 0)
 #define thread_extension_discover_response_tlv_write(data, version, securityPolicy) ((void) 0)
-#define thread_extension_service_init(cur) (0)
+#define thread_extension_service_init(cur) ((void) 0)
 #define thread_extension_joining_enabled(interface_id) (false)
 #define thread_extension_discover_response_len(cur) (0)
 #define thread_extension_discover_response_write(cur, ptr) (ptr)

source/6LoWPAN/Thread/thread_router_bootstrap.c

@@ -1407,6 +1407,7 @@ static void thread_address_registration_tlv_parse(uint8_t *ptr, uint16_t data_le
                 //Register GP --> 16
                 int retVal = thread_nd_address_registration(cur, tempIPv6Address, mac16, cur->mac_parameters->pan_id, mac64, &new_neighbour_created);
                 thread_extension_address_registration(cur, tempIPv6Address, mac64, new_neighbour_created, retVal == -2);
+               (void) retVal;
             } else {
                 tr_debug("No Context %u", ctxId);
             }
@@ -1427,6 +1428,7 @@ static void thread_address_registration_tlv_parse(uint8_t *ptr, uint16_t data_le
                 //Register GP --> 16
                 int retVal = thread_nd_address_registration(cur, ptr, mac16, cur->mac_parameters->pan_id, mac64, &new_neighbour_created);
                 thread_extension_address_registration(cur, ptr, mac64, new_neighbour_created, retVal == -2);
+               (void) retVal;
             }
 
             ptr += 16;

source/Common_Protocols/icmpv6.c

@@ -1092,7 +1092,7 @@ buffer_t *icmpv6_up(buffer_t *buf)
                 buf = rpl_control_source_route_error_handler(buf, cur);
             }
 #endif
-        /* no break */
+        /* fall through */
 
         default:
             if (buf) {