[PATCH 3/3] net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls

RCU was added to UDP lookups, using a fast infrastructure :
- sockets kmem_cache use SLAB_DESTROY_BY_RCU and dont pay the
  price of call_rcu() at freeing time.
- hlist_nulls permits to use few memory barriers.

This patch uses same infrastructure for TCP/DCCP established
and timewait sockets.

Thanks to SLAB_DESTROY_BY_RCU, no slowdown for applications
using short lived TCP connections. A followup patch, converting
rwlocks to spinlocks will even speedup this case.

__inet_lookup_established() is pretty fast now we dont have to
dirty a contended cache line (read_lock/read_unlock)

Only established and timewait hashtable are converted to RCU
(bind table and listen table are still using traditional locking)

Signed-off-by: Eric Dumazet <redacted>
---
 include/net/inet_hashtables.h    |    4 -
 include/net/inet_timewait_sock.h |   10 +--
 net/core/sock.c                  |    4 +
 net/dccp/ipv4.c                  |    1
 net/dccp/ipv6.c                  |    1
 net/dccp/proto.c                 |    4 -
 net/ipv4/inet_diag.c             |    6 +-
 net/ipv4/inet_hashtables.c       |   78 ++++++++++++++++++++---------
 net/ipv4/inet_timewait_sock.c    |   26 +++++----
 net/ipv4/tcp.c                   |    4 -
 net/ipv4/tcp_ipv4.c              |   25 ++++-----
 net/ipv6/inet6_hashtables.c      |   70 +++++++++++++++++---------
 net/ipv6/tcp_ipv6.c              |    1
 13 files changed, 150 insertions(+), 84 deletions(-)