Merge branch 'mptcp-don-t-auto-adjust-rcvbuf-size-if-locked'

Florian Westphal says:

====================
mptcp: don't auto-adjust rcvbuf size if locked

The mptcp receive buffer is auto-sized based on the subflow receive
buffer.  Don't do this if userspace specfied a value via SO_RCVBUF
setsockopt.

Also update selftest program to provide a new option to set a fixed
size.
====================

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