net/socket: Fix compiler warning (regression for MinGW)

Commit 213fd5087e removed a type cast
which is needed for MinGW:

net/socket.c:136: warning:
 pointer targets in passing argument 2 of ‘sendto’ differ in signedness
/usr/lib/gcc/amd64-mingw32msvc/4.4.4/../../../../amd64-mingw32msvc/include/winsock2.h:1313: note:
 expected ‘const char *’ but argument is of type ‘const uint8_t *’

Add a 'qemu_sendto' macro which provides that type cast where needed
and use the new macro instead of 'sendto'.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>

net/socket.c

@@ -131,9 +131,9 @@ static ssize_t net_socket_receive_dgram(NetClientState *nc, const uint8_t *buf,
     ssize_t ret;
 
     do {
-        ret = sendto(s->fd, buf, size, 0,
-                     (struct sockaddr *)&s->dgram_dst,
-                     sizeof(s->dgram_dst));
+        ret = qemu_sendto(s->fd, buf, size, 0,
+                          (struct sockaddr *)&s->dgram_dst,
+                          sizeof(s->dgram_dst));
     } while (ret == -1 && errno == EINTR);
 
     if (ret == -1 && errno == EAGAIN) {

qemu-common.h

@@ -223,9 +223,14 @@ int qemu_pipe(int pipefd[2]);
 #endif
 
 #ifdef _WIN32
+/* MinGW needs a type cast for the 'buf' argument. */
 #define qemu_recv(sockfd, buf, len, flags) recv(sockfd, (void *)buf, len, flags)
+#define qemu_sendto(sockfd, buf, len, flags, destaddr, addrlen) \
+    sendto(sockfd, (const void *)buf, len, flags, destaddr, addrlen)
 #else
 #define qemu_recv(sockfd, buf, len, flags) recv(sockfd, buf, len, flags)
+#define qemu_sendto(sockfd, buf, len, flags, destaddr, addrlen) \
+    sendto(sockfd, buf, len, flags, destaddr, addrlen)
 #endif
 
 /* Error handling.  */