net: factor tap_read_packet() out of tap_send()

Move portability clutter out into its own function.
Signed-off-by: NMark McLoughlin <markmc@redhat.com>

net.c

@@ -951,21 +951,31 @@ static void tap_receive(void *opaque, const uint8_t *buf, int size)
     }
 }
 
-static void tap_send(void *opaque)
-{
-    TAPState *s = opaque;
-    uint8_t buf[4096];
-    int size;
-
 #ifdef __sun__
+static ssize_t tap_read_packet(int tapfd, uint8_t *buf, int maxlen)
+{
     struct strbuf sbuf;
     int f = 0;
-    sbuf.maxlen = sizeof(buf);
+
+    sbuf.maxlen = maxlen;
     sbuf.buf = (char *)buf;
-    size = getmsg(s->fd, NULL, &sbuf, &f) >=0 ? sbuf.len : -1;
+
+    return getmsg(tapfd, NULL, &sbuf, &f) >= 0 ? sbuf.len : -1;
+}
 #else
-    size = read(s->fd, buf, sizeof(buf));
+static ssize_t tap_read_packet(int tapfd, uint8_t *buf, int maxlen)
+{
+    return read(tapfd, buf, maxlen);
+}
 #endif
+
+static void tap_send(void *opaque)
+{
+    TAPState *s = opaque;
+    uint8_t buf[4096];
+    int size;
+
+    size = tap_read_packet(s->fd, buf, sizeof(buf));
     if (size > 0) {
         qemu_send_packet(s->vc, buf, size);
     }