net: use symbolic values for ndo_start_xmit() return codes

Convert magic values 1 and -1 to NETDEV_TX_BUSY and NETDEV_TX_LOCKED respectively.

0 (NETDEV_TX_OK) is not changed to keep the noise down, except in very few cases
where its in direct proximity to one of the other values.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 364222b..d238a89 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1615,7 +1615,7 @@
 {
 	struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 	struct ieee80211_local *local = sdata->local;
-	int ret = 1, head_need;
+	int ret = NETDEV_TX_BUSY, head_need;
 	u16 ethertype, hdrlen,  meshhdrlen = 0;
 	__le16 fc;
 	struct ieee80211_hdr hdr;