refactor: Use enum-specific pack functions for enum values.

[iphydf]

It's more obvious this way.

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This change is 

[codecov]

Codecov Report

Attention: 24 lines in your changes are missing coverage. Please review.

Comparison is base (afc4724) 66.98% compared to head (e2c01e4) 66.90%.

Files	Patch %	Lines
toxcore/tox_pack.c	45.45%	6 Missing ⚠️
toxcore/events/group_join_fail.c	0.00%	2 Missing ⚠️
toxcore/events/group_message.c	0.00%	2 Missing ⚠️
toxcore/events/group_moderation.c	0.00%	2 Missing ⚠️
toxcore/events/group_peer_exit.c	0.00%	2 Missing ⚠️
toxcore/events/group_peer_status.c	0.00%	2 Missing ⚠️
toxcore/events/group_privacy_state.c	0.00%	2 Missing ⚠️
toxcore/events/group_private_message.c	0.00%	2 Missing ⚠️
toxcore/events/group_topic_lock.c	0.00%	2 Missing ⚠️
toxcore/events/group_voice_state.c	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2567      +/-   ##
==========================================
- Coverage   66.98%   66.90%   -0.09%     
==========================================
  Files         146      147       +1     
  Lines       30205    30177      -28     
==========================================
- Hits        20233    20190      -43     
- Misses       9972     9987      +15     

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