Define (missing) hash message size for SHA1.

Define hashing size constants specific to TCP cookies, and add new function.

Maintain global secret values for tcp_cookie_generator().

This is a significantly revised implementation of earlier (15-year-old)
Photuris [RFC-2522] code for the KA9Q cooperative multitasking platform.

Linux RCU technique appears to be well-suited to this application, though
neither of the circular queue items are freed.

These functions will also be used in subsequent patches that implement
additional features.

Signed-off-by: William.Allen.Simpson@gmail.com
---
  include/linux/cryptohash.h |    1 +
  include/net/tcp.h          |    8 +++
  net/ipv4/tcp.c             |  146 ++++++++++++++++++++++++++++++++++++++++++++
  3 files changed, 155 insertions(+), 0 deletions(-)