crypto/tls: replace tls Conn's rawInput with a small buffer when Read timeout

[cch123]

fixes #43563

[cch123]

I'll add more benchmark data later

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[cch123]

code demos is in #43563
server side read timeout value is 5 seconds

before optimization, 20k connections, 16k request size，500 qps：

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
11397 root      20   0 1722816 1.181g   3712 S  16.3 15.5   0:29.03 c
11367 root      20   0 1937180 1.053g   2744 S  17.3 13.8   1:01.31 s -----> this is the server process

cost totally 1g+ memory

after optimization, 20k conns, 16k request size，500 qps：

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
22618 root      20   0 1491180 1.135g   4276 S  16.9 14.9   0:26.76 c
22610 root      20   0 1528452 691064   3444 S  18.9  8.6   1:01.26 s_opt -----> this is the server process

about 700M memory

Since I don't have a good enough server for more connections to test now.... I can't provide data for more than 20k connections currently

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This PR (HEAD: 51de0f8) has been imported to Gerrit for code review.

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Message from ChunHui Cao:

Patch Set 4:

(1 comment)

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