Add LAN_discovery to the list of apidsl-generated files.

[iphydf]

So it gets regenerated when the .api.h file changes.

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This change is 

[codecov]

Codecov Report

Merging #1206 into master will increase coverage by 0.1%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #1206     +/-   ##
========================================
+ Coverage    82.7%   82.9%   +0.1%     
========================================
  Files          82      82             
  Lines       14647   14647             
========================================
+ Hits        12117   12144     +27     
+ Misses       2530    2503     -27

Impacted Files	Coverage Δ
toxcore/LAN_discovery.c	83% <0%> (-2.9%)	⬇️
toxcore/friend_connection.c	93.9% <0%> (-0.6%)	⬇️
toxcore/DHT.c	76.7% <0%> (ø)	⬆️
toxcore/onion_client.c	96.1% <0%> (+0.1%)	⬆️
toxcore/net_crypto.c	94.3% <0%> (+0.7%)	⬆️
toxav/toxav.c	68.5% <0%> (+1.4%)	⬆️
toxav/msi.c	65.6% <0%> (+1.9%)	⬆️
auto_tests/toxav_many_test.c	96.6% <0%> (+4%)	⬆️

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[hugbubby]

Reviewed 2 of 2 files at r1.
Reviewable status: 0 of 1 approvals obtained