net: re-name vc->fd_read() to vc->receive()

VLANClientState's fd_read() handler doesn't read from file
descriptors, it adds a buffer to the client's receive queue.

Re-name the handlers to make things a little less confusing.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>

tap-win32.c

@@ -650,7 +650,7 @@ static void tap_cleanup(VLANClientState *vc)
     qemu_free(s);
 }
 
-static void tap_receive(void *opaque, const uint8_t *buf, int size)
+static void tap_receive(void *opaque, const uint8_t *buf, size_t size)
 {
     TAPState *s = opaque;