Make the sys_arch_protect() mutex be recursive.

Fixes #9744

Author: Paul Thompson

features/lwipstack/lwip-sys/arch/lwip_sys_arch.c

@@ -432,6 +432,7 @@ void sys_init(void) {
     lwip_sys_mutex_attr.name = "lwip_sys_mutex";
     lwip_sys_mutex_attr.cb_mem = &lwip_sys_mutex_data;
     lwip_sys_mutex_attr.cb_size = sizeof(lwip_sys_mutex_data);
+    lwip_sys_mutex_attr.attr_bits = osMutexPrioInherit | osMutexRecursive;
     lwip_sys_mutex = osMutexNew(&lwip_sys_mutex_attr);
     if (lwip_sys_mutex == NULL)
         MBED_ERROR(MBED_MAKE_ERROR(MBED_MODULE_NETWORK_STACK, MBED_ERROR_CODE_INITIALIZATION_FAILED), "sys_init error, mutex initialization failed\n");