datapath: backport: ip_tunnel: Move stats update to iptunnel_xmit()

datapath: backport: ip_tunnel: Move stats update to iptunnel_xmit()

Upstream commit:
    commit 039f50629b7f860f36644ed1f34b27da9aa62f43
    Author: Pravin B Shelar <pshelar@ovn.org>

    ip_tunnel: Move stats update to iptunnel_xmit()

    By moving stats update into iptunnel_xmit(), we can simplify
    iptunnel_xmit() usage. With this change there is no need to
    call another function (iptunnel_xmit_stats()) to update stats
    in tunnel xmit code path.

    Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
Acked-by: Jesse Gross <jesse@kernel.org>