tried to add basic socket unit tests (nonsense only for now); made LOCK_TCPIP_CORE()/UNLOCK_TCPIP_CORE() overridable for that

test/unit/lwip_unittests.c

@@ -8,6 +8,7 @@
 #include "etharp/test_etharp.h"
 #include "dhcp/test_dhcp.h"
 #include "mdns/test_mdns.h"
+#include "api/test_sockets.h"
 
 #include "lwip/init.h"
 
@@ -44,7 +45,8 @@ int main(void)
     pbuf_suite,
     etharp_suite,
     dhcp_suite,
-    mdns_suite
+    mdns_suite,
+    sockets_suite
   };
   size_t num = sizeof(suites)/sizeof(void*);
   LWIP_ASSERT("No suites defined", num > 0);