fix(exhook): ensuring that exhook dispatches the client events are sequential

[HJianBo]

porting by: #8311

[coveralls]

Pull Request Test Coverage Report for Build 2711651958

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• 37 unchanged lines in 9 files lost coverage.
• Overall coverage decreased (-0.0006%) to 78.802%

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Files with Coverage Reduction	New Missed Lines	%
apps/emqx_bridge/src/emqx_bridge.erl	1	85.11%
apps/emqx/src/emqx_authentication_config.erl	1	84.75%
apps/emqx/src/emqx_cm.erl	1	88.99%
apps/emqx_gateway/src/mqttsn/emqx_sn_frame.erl	2	64.04%
apps/emqx_authn/src/emqx_authn.erl	3	77.78%
apps/emqx_dashboard/src/emqx_dashboard_listener.erl	4	74.63%
apps/emqx/src/emqx_channel.erl	5	85.53%
apps/emqx/src/emqx_sys_mon.erl	6	86.46%
apps/emqx/src/emqx_reason_codes.erl	14	86.03%

Totals
Change from base Build 2710777825:	-0.0006%
Covered Lines:	20825
Relevant Lines:	26427

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💛 - Coveralls