netdevsim: Fix build error without CONFIG_INET

If CONFIG_INET is not set, building fails:

drivers/net/netdevsim/dev.o: In function `nsim_dev_trap_report_work':
dev.c:(.text+0x67b): undefined reference to `ip_send_check'

Use ip_fast_csum instead of ip_send_check to avoid
dependencies on CONFIG_INET.
Reported-by: NHulk Robot <hulkci@huawei.com>
Fixes: da58f90f ("netdevsim: Add devlink-trap support")
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Acked-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: NIdo Schimmel <idosch@mellanox.com>
Tested-by: NIdo Schimmel <idosch@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/netdevsim/dev.c

@@ -389,7 +389,8 @@ static struct sk_buff *nsim_dev_trap_skb_build(void)
 	iph->ihl = 0x5;
 	iph->tot_len = htons(tot_len);
 	iph->ttl = 100;
-	ip_send_check(iph);
+	iph->check = 0;
+	iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
 
 	udph = skb_put_zero(skb, sizeof(struct udphdr) + data_len);
 	get_random_bytes(&udph->source, sizeof(u16));