arp: make arp_hdr_len() return unsigned int

Negative ARP header length are not a thing.

Constify arguments while I'm at it.

Space savings:

	add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-3 (-3)
	function                        old     new   delta
	arpt_do_table                  1163    1160      -3
Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -2491,7 +2491,8 @@ int bond_arp_rcv(const struct sk_buff *skb, struct bonding *bond,
 	struct slave *curr_active_slave, *curr_arp_slave;
 	unsigned char *arp_ptr;
 	__be32 sip, tip;
-	int alen, is_arp = skb->protocol == __cpu_to_be16(ETH_P_ARP);
+	int is_arp = skb->protocol == __cpu_to_be16(ETH_P_ARP);
+	unsigned int alen;
 
 	if (!slave_do_arp_validate(bond, slave)) {
 		if ((slave_do_arp_validate_only(bond) && is_arp) ||

include/linux/if_arp.h

@@ -31,7 +31,7 @@ static inline struct arphdr *arp_hdr(const struct sk_buff *skb)
 	return (struct arphdr *)skb_network_header(skb);
 }
 
-static inline int arp_hdr_len(struct net_device *dev)
+static inline unsigned int arp_hdr_len(const struct net_device *dev)
 {
 	switch (dev->type) {
 #if IS_ENABLED(CONFIG_FIREWIRE_NET)