Fix typos in comments and log and test assertion messages.

[yangfl]

This change is 

[iphydf]

Reviewed 13 of 13 files at r1.
Reviewable status: 0 of 1 approvals obtained

[codecov]

Codecov Report

Merging #1187 into master will decrease coverage by 0.2%.
The diff coverage is 33.3%.

@@           Coverage Diff            @@
##           master   #1187     +/-   ##
========================================
- Coverage    82.8%   82.5%   -0.3%     
========================================
  Files          82      82             
  Lines       14637   14637             
========================================
- Hits        12124   12089     -35     
- Misses       2513    2548     +35

Impacted Files	Coverage Δ
toxcore/onion.c	98.7% <ø> (ø)	⬆️
toxcore/DHT.c	76.6% <ø> (ø)	⬆️
testing/misc_tools.c	55.1% <ø> (ø)	⬆️
toxav/rtp.c	72.6% <ø> (ø)	⬆️
auto_tests/TCP_test.c	100% <ø> (ø)	⬆️
toxcore/crypto_core_test.cc	90.3% <0%> (ø)	⬆️
toxav/toxav.c	67.3% <100%> (-1%)	⬇️
auto_tests/network_test.c	90.3% <0%> (-7.3%)	⬇️
auto_tests/toxav_many_test.c	92.5% <0%> (-4.1%)	⬇️
auto_tests/toxav_basic_test.c	81.6% <0%> (-2%)	⬇️
... and 5 more

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