[TCP] IPV6 : Change a divide into a right shift in tcp_v6_send_ack()

[Eric Dumazet <dada1@cosmosbay.com>]

[-- Attachment #1: Type: text/plain, Size: 211 bytes --]

Because tot_len is signed in tcp_v6_send_ack(), tot_len/4 forces compiler
to emit an integer divide, while we can help it to use a right shift,
less expensive.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

[-- Attachment #2: tcp_ipv6.patch --]
[-- Type: text/plain, Size: 415 bytes --]

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 0268e11..92f0fda 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1124,7 +1124,7 @@ static void tcp_v6_send_ack(struct tcp_timewait_sock *tw,
 	memset(t1, 0, sizeof(*t1));
 	t1->dest = th->source;
 	t1->source = th->dest;
-	t1->doff = tot_len/4;
+	t1->doff = tot_len >> 2;
 	t1->seq = htonl(seq);
 	t1->ack_seq = htonl(ack);
 	t1->ack = 1;