RTC: Fix nack encode seqnum

[xiaofeilong]

No description provided.

[xiaozhihong]

Thank you for submitting. Can you please provide a uTest? This way, we will never encounter any issues with future changes and we can also verify that the modified code is working correctly.

TRANS_BY_GPT3

[codecov-commenter]

Codecov Report

Merging #2766 (e9ef536) into 4.0release (5ccd63d) will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           4.0release    #2766      +/-   ##
==============================================
+ Coverage       60.15%   60.32%   +0.16%     
==============================================
  Files             121      121              
  Lines           50949    50970      +21     
==============================================
+ Hits            30648    30747      +99     
+ Misses          20301    20223      -78     

| Impacted Files | Coverage Δ | |'

Translated to English while maintaining the markdown structure:

'| Impacted Files | Coverage Δ | |
|---|---|---|
| trunk/src/kernel/srs_kernel_rtc_rtcp.cpp | 15.51% <100.00%> (+10.27%) | ⬆️ |
| trunk/src/utest/srs_utest_rtc.cpp | 99.40% <100.00%> (+0.01%) | ⬆️ |
| trunk/src/kernel/srs_kernel_rtc_rtp.hpp | 54.54% <0.00%> (+9.09%) | ⬆️ |

---

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TRANS_BY_GPT3

[xiaozhihong]

rtcpNack_encode, rtcpNack_decode, It is better to name them consistently with the style of srs, so change them to rtcp_nack_encode, rtcp_nack_decode would be better.

TRANS_BY_GPT3

[winlinvip]

@xiaofeilong @xiaozhihong 👍