neotest part pending.

compared to tgro5:

tgro0   py -> noise (ZEO, NEO/pylite, NEO/pysql, partly neo/go)
tgro10  py=no-noise, tpy~=tgro5; tgo serial~same, +prefetch more noise (?) 40|65
tgro15  lat_tcp 1B 49->45 sometime (consistently) otherwise more-or-less same
tgro20  lat_tcp 4K 170µs->167µs (c)
tgro25  lat_tcp 4K 170µs->167µs (c), lat_tcp 4K 175 -> 171µs (go)
        ZEOv a bit
        go-go + prefetch !sha1 -> noise + higher (~65µs -> 70 - 110µs)

txc40µs4f seems to be worse than txc200µs4f

Link and TCP* latencies are ~ same and stable.

Compared to b288e62f py timings stabilize:

ZEO		~580-1045μs	-> 585µs
NEO/pylite	~600-700μs	-> ~550-570µs	(Cpy)
NEO/pylite	~525-580μs	-> ~450µs	(Cgo)
NEO/pysql	~820-930μs	-> ~840µs	(Cpy)
NEO/pysql	~740-800μs	-> ~740µs	(Cgo)

Go timings get a bit worse:

NEO/go		~360µs		-> ~380µs	(Cpy)
NEO/go		~160µs		-> ~165-170µs	(Cgo)
NEO/go-nosha1	~140µs		-> ~150µs

Compared to 15a9ccef go+pretech128 timings stabilize:

go-go+prefetch128		~65-160µs	-> ~40-45µs, 60µs(x1)
go-go+prefetch128 (!sha1)	~60-150µs	-> ~60µs,    40µs(x1)

Compared to run from Oct10 txc settings were not changed and they are now
200μs/4f/0μs-irq/0f-irq on both machines instead of 200μs/4f/0μs-irq/0f-irq on
neo1 and 200μs/0f/0μs-irq/0f-irq on neo2.

The noise about py runs remains.

Go-go serial time remains the same ~155μs without much noise, but Go-go time
with +prefetch128 gets worse:

NEO/go Cgo +prefetch128

        ~45μs   -> 65 - 160μs

Probably it makes sense to tune txc too...

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.

On neo1 - neo2 without TSO latency becomes very poor in lat_tcp when
payload size becomes greater TCP MSS (lat_tcp -m 1448 ~ 130μs; lat_tcp
-m 1449 ~ 500μs and more)

e.g.

	neotest cpustat ls

Same a before with added information.
In particular z6001-z600 shows there is no TCP RR step-wise 400μs increase
while going 1400B -> 1500B as it is currently the case on RTL.

Same as before but with more information and adjusted ping and TCP RR.

In particular TCP RR shows:

TCPRR1400	~ 120μs
TCPRR1500	~ 430μs

The time when this increases step-wise is when TCP packet crosses fitting 1 ethernet frame.
It does not happen on z600* with their current settings.

Same as Oct05 5μs C-latency with added:

- pystones
- t(sha1) py & go
- zhash.go working in prefetch mode
- 16 clients loading 1 server at the same time