MB-11259: send window update size in ext field
MB-11259: send window update size in ext field

Mike said it's because we usually send fixed-size things in ext and
body is usually for variable-sized things.

This depends on corresponding memcached commit here:
http://review.couchbase.org/37746

Change-Id: I727e8febce13dbd6289823df1e6389df4bdacf2f
Reviewed-on: http://review.couchbase.org/38767
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Michael Wiederhold <a17fed27eaa842282862ff7c1b9c8395a26ac320@couchbase.com>

t3rm1n4l/ns_server,membase/ns_server,membase/ns_server,nimishzynga/ns_server,ceejatec/ns_server,nimishzynga/ns_server,membase/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,membase/ns_server,ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,mschoch/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,mschoch/ns_server,mschoch/ns_server,membase/ns_server,mschoch/ns_server,ceejatec/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server