net: dsa: tag_rtl4_a: Fix egress tags

I noticed that only port 0 worked on the RTL8366RB since we
started to use custom tags.

It turns out that the format of egress custom tags is actually
different from ingress custom tags. While the lower bits just
contain the port number in ingress tags, egress tags need to
indicate destination port by setting the bit for the
corresponding port.

It was working on port 0 because port 0 added 0x00 as port
number in the lower bits, and if you do this the packet appears
at all ports, including the intended port. Ooops.

Fix this and all ports work again. Use the define for shifting
the "type A" into place while we're at it.

Tested on the D-Link DIR-685 by sending traffic to each of
the ports in turn. It works.

Fixes: 86dd9868 ("net: dsa: tag_rtl4_a: Support also egress tags")
Cc: DENG Qingfang <dqfext@gmail.com>
Cc: Mauri Sandberg <sandberg@mailfence.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/tag_rtl4_a.c

@@ -54,9 +54,10 @@ static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
 	p = (__be16 *)tag;
 	*p = htons(RTL4_A_ETHERTYPE);
 
-	out = (RTL4_A_PROTOCOL_RTL8366RB << 12) | (2 << 8);
-	/* The lower bits is the port number */
-	out |= (u8)dp->index;
+	out = (RTL4_A_PROTOCOL_RTL8366RB << RTL4_A_PROTOCOL_SHIFT) | (2 << 8);
+	/* The lower bits indicate the port number */
+	out |= BIT(dp->index);
+
 	p = (__be16 *)(tag + 2);
 	*p = htons(out);