Merge branch 'net-better-const'

Eric Dumazet says:

====================
net: better const qualifier awareness

This is a follow-up of d27d367d ("inet: better const qualifier awareness")

Adopting container_of_const() to perform (struct sock *)->(protocol sock *)
operation is allowing us to propagate const qualifier and thus detect
misuses at compile time.

Most conversions are trivial, because most protocols did not adopt yet
const sk pointers where it could make sense.

Only mptcp and tcp patches (end of this series) are requiring small
adjustments.
====================

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