Avoid recursion in ip_is_lan and ip_is_local.

[iphydf]

This change is 

[codecov]

Codecov Report

Merging #1139 into master will decrease coverage by 0.2%.
The diff coverage is 72.7%.

@@           Coverage Diff            @@
##           master   #1139     +/-   ##
========================================
- Coverage    82.9%   82.6%   -0.3%     
========================================
  Files          82      82             
  Lines       14594   14476    -118     
========================================
- Hits        12104   11971    -133     
- Misses       2490    2505     +15

Impacted Files	Coverage Δ
toxcore/LAN_discovery.c	84.9% <72.7%> (ø)	⬆️
auto_tests/network_test.c	90.3% <0%> (-7.3%)	⬇️
toxcore/group.c	73.2% <0%> (-2.9%)	⬇️
auto_tests/conference_test.c	97.7% <0%> (-1.5%)	⬇️
toxcore/net_crypto.c	92.7% <0%> (-1.5%)	⬇️
toxcore/onion_client.c	94.5% <0%> (-1.4%)	⬇️
toxcore/friend_connection.c	94.5% <0%> (-0.3%)	⬇️
toxcore/DHT.c	76.7% <0%> (-0.1%)	⬇️
toxcore/tox.c	65.7% <0%> (-0.1%)	⬇️
auto_tests/run_auto_test.h	100% <0%> (ø)	⬆️
... and 3 more

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