http: handle and print socket errors

vlib/net/init_nix.v

@@ -4,5 +4,10 @@ module net
 #include <unistd.h>
 #include <netinet/in.h>
 #include <netdb.h>
+#include <errno.h>
 
 fn init() int { return 1 }
+
+fn error_code() int {
+    return C.errno
+}