Merge branch 'listener_refactor_part_15'

Eric Dumazet says:

====================
tcp listener refactoring part 15

I am trying to make the final patch pushing request socks into ehash
as small as possible. In this patch series, I made various adjustments
for the SYNACK generation, allowing me to reach 1 Mpps SYNACK in my
stress test (still hitting LISTENER spinlock of course, and the syn_wait
spinlock)

I also converted the ICMP handlers a bit ahead of time :

They no longer need to get the LISTENER socket, and can use
only a lookup in ehash table. No big deal if we ignore ICMP
for requests socks before the final steps.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>