net: sk_pacing_shift_update() helper

In commit 3a9b76fd0db9 ("tcp: allow drivers to tweak TSQ logic")
I gave a code sample to set sk->sk_pacing_shift that was not complete.

Better add a helper that can be used by drivers without worries,
and maybe amended in the future.

A wifi driver might use it from its ndo_start_xmit()

Following call would setup TCP to allow up to ~8ms of queued data per
flow.

sk_pacing_shift_update(skb->sk, 7);

CRs-Fixed: 2156182
Change-Id: Id1675d3183004e8ba6eee4f7b1c7ba56124b696b
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Git-commit: c9f1f58dc2eba550f208809d272bf0b14f41edba
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>