Implement ipc_netsockdelete() syscall and automatic dangling socket cleanup

user/diagdummy/tcptest.c

@@ -4,7 +4,7 @@
 
 #define MAX_CONNS 10
 
-void diagdummy_tcptest(void) {
+void diagdummy_tcptestserver(void) {
   netsock_t netsock = ipc_netsockmake(NETSOCK_IPV4, NETSOCK_TCP, 1);
   ipc_netsocklisten(netsock, MAX_CONNS);
 
@@ -16,4 +16,10 @@ void diagdummy_tcptest(void) {
     } else {
     }
   }
+
+  ipc_netsockdelete(netsock);
+}
+
+void diagdummy_tcptestclient(void) {
+
 }