Merge branch 'listener_refactor_16'

Eric Dumazet says:

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tcp: listener refactor part 16

A CONFIG_PROVE_RCU=y build revealed an RCU splat I had to fix.

I added const qualifiers to various md5 methods, as I expect
to call them on behalf of request sock traffic even if
the listener socket is not locked. This seems ok, but adding
const makes the contract clearer. Note a good reduction
of code size thanks to request/establish sockets convergence.
====================

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