Use bool for IPv6 flag in test programs and DHT_bootstrap.

[iphydf]

This change is 

[hugbubby]

Reviewed 5 of 5 files at r1.
Reviewable status: 0 of 1 approvals obtained

[codecov]

Codecov Report

Merging #1231 into master will decrease coverage by 0.2%.
The diff coverage is 0%.

@@           Coverage Diff            @@
##           master   #1231     +/-   ##
========================================
- Coverage    83.1%   82.8%   -0.3%     
========================================
  Files          82      82             
  Lines       14692   14647     -45     
========================================
- Hits        12214   12139     -75     
- Misses       2478    2508     +30

Impacted Files	Coverage Δ
testing/misc_tools.c	55.1% <0%> (ø)	⬆️
toxcore/TCP_server.c	75.9% <0%> (-4.4%)	⬇️
toxav/toxav.c	67.3% <0%> (-0.7%)	⬇️
toxcore/Messenger.c	86.5% <0%> (-0.7%)	⬇️
toxav/msi.c	63.9% <0%> (-0.3%)	⬇️
toxcore/DHT.c	76.6% <0%> (-0.3%)	⬇️
toxcore/onion_client.c	95.9% <0%> (-0.2%)	⬇️
toxcore/network.c	82.3% <0%> (+0.2%)	⬆️
toxcore/friend_connection.c	94.5% <0%> (+0.2%)	⬆️
auto_tests/save_load_test.c	98.6% <0%> (+0.5%)	⬆️
... and 1 more

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