[ROCKETMQ-355] Client asyncSend is not fully async

[lindzh]

What is the purpose of the change

Client asyncSend is not fully async because of param validation, connection status check and get route info may cause exception,and these exceptions is called in user thread may cause biz stop.

Brief changelog

Make client asyncSend fully async.

Verifying this change

This is a trivial change.

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[coveralls]

Coverage increased (+0.2%) to 40.138% when pulling 0e09e26 on lindzh:fix_asyncSend into a096580 on apache:develop.

[zhouxinyu]

Hi @lindzh , No need to close the previous PR and open a new, while the comments will be lost.

[lindzh]

@zhouxinyu,yeah, keep comment is a good idea for continuous develop. At first I want to limit the send request and using network semaphore as send signal,but after doing that I found it was a mistake and open another PR for concise and speed.

[vongosling]

Thanks @lindzh . I have noticed another PR for this question
#318, I am willing to help guys to polish the modification. Let's work together in the new PR.