NanostackInterface: Check input address is IPv6

For the two calls that use the address - sendto and connect, check that it
actually is an IPv6 address.

Author: kjbracey

features/nanostack/FEATURE_NANOSTACK/nanostack-interface/NanostackInterface.cpp

@@ -716,6 +716,10 @@ int NanostackInterface::socket_sendto(void *handle, const SocketAddress &address
         return NSAPI_ERROR_NO_SOCKET;
     }
 
+    if (address.get_ip_version() != NSAPI_IPv6) {
+        return NSAPI_ERROR_UNSUPPORTED;
+    }
+
     nanostack_lock();
 
     int ret;
@@ -849,6 +853,10 @@ int NanostackInterface::socket_connect(void *handle, const SocketAddress &addr)
         return NSAPI_ERROR_NO_SOCKET;
     }
 
+    if (addr.get_ip_version() != NSAPI_IPv6) {
+        return NSAPI_ERROR_UNSUPPORTED;
+    }
+
     nanostack_lock();
 
     int ret;