AP_HAL: fixed socket destructor

libraries/AP_HAL/utility/Socket.cpp

@@ -35,8 +35,9 @@ datagram(_datagram)
 
 SocketAPM::~SocketAPM()
 {
-    if (::close(fd) < 0) {
-        perror("close");
+    if (fd != -1) {
+        ::close(fd);
+        fd = -1;
     }
 }
 

libraries/AP_HAL/utility/Socket.h

@@ -47,7 +47,7 @@ public:
 
 private:
     bool datagram;
-    int fd;
+    int fd = -1;
 
     void make_sockaddr(const char *address, uint16_t port, struct sockaddr_in &sockaddr);
 };