net: make struct net_device::min_header_len 8-bit

This field is never big enough to warrant 16-bitness.

8-bit accesses enjoy shorted encoding on i386/x86_64 than 16-bit accesses:

add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-10 (-10)
function old new delta
loopback_setup 169 164 -5
ether_setup 148 143 -5

---

 include/linux/netdevice.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -1715,7 +1715,7 @@ struct net_device {
 	unsigned int		max_mtu;
 	unsigned short		type;
 	unsigned short		hard_header_len;
-	unsigned short		min_header_len;
+	unsigned char		min_header_len;
 
 	unsigned short		needed_headroom;
 	unsigned short		needed_tailroom;

From: Alexey Dobriyan <[email protected]>
Date: Mon, 10 Apr 2017 11:25:26 +0300

Applied.