Merge branch 'mptcp-optimizations'

Mat Martineau says:

====================
mptcp: A few optimizations

Here is a set of patches that we've accumulated and tested in the MPTCP
tree.

Patch 1 removes the MPTCP-level tx skb cache that added complexity but
did not provide a meaningful benefit.

Patch 2 uses the fast socket lock in more places.

Patch 3 improves handling of a data-ready flag.

Patch 4 deletes an unnecessary and racy connection state check.

Patch 5 adds a MIB counter for one type of invalid MPTCP header.

Patch 6 improves self test failure output.
====================

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