See previous commit for details about why latency is bad for TCP payload > MSS
without TSO.

Compared to latest neo1-neo2 timings from Oct05 (C-states disabled, no
rx-delay) it improves:

TCP1             ~45μs  ->   ~45μs
TCP1472         ~430μs			# TCP lat. anaomaly
TCP1400                 ->  ~120μs	# finally
TCP1500                 ->  ~130μs	# fixed
TCP4096         ~285μs  ->  ~170μs	# !

ZEO             ~670μs  ->  ~580-1045μs (?)
NEO/pylite      ~605μs  ->  ~600-700μs  (?)     (Cpy)
NEO/pylite      ~505μs  ->  ~525-580μs  (?)     (Cgo)
NEO/pysql       ~900μs  ->  ~820-930μs  (?)     (Cpy)
NEO/pysql       ~780μs  ->  ~740-800μs  (?)     (Cgo)
NEO/go          ~430μs  ->  ~360μs              (Cpy)	# <-- NOTE
NEO/go          ~210μs  ->  ~160μs              (Cgo)	# <-- NOTE
NEO/go-nosha1   ~190μs  ->  ~140μs			# <-- NOTE

not sure about noise in pure py runs but given raw tcp latency absolutely
improves this should be a good change to make.