chore(p2p): decrease p2p.max_enabled_sync's default value: 16 -> 8

[jansegre]

Motivation

The default value of 16 can be slower than expected in certain cases.

Acceptance Criteria

• Reduce the default value to 8, it can still be adjusted through the settings and even in runtime through sysctl.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[github-actions]

Bencher Report

Branch	chore/reduce-max-enabled-sync
Testbed	ubuntu-22.04

Click to view all benchmark results

Benchmark	Latency	Benchmark Result minutes (m) (Result Δ%)	Lower Boundary minutes (m) (Limit %)	Upper Boundary minutes (m) (Limit %)
sync-v2 (up to 20000 blocks)	📈 view plot 🚷 view threshold	1.52 (-8.55%)	1.49 (98.42%)	1.82 (83.13%)

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.94%. Comparing base (692a74c) to head (9247743).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1199   +/-   ##
=======================================
  Coverage   84.93%   84.94%           
=======================================
  Files         323      323           
  Lines       25124    25124           
  Branches     3859     3859           
=======================================
+ Hits        21340    21342    +2     
+ Misses       3041     3039    -2     
  Partials      743      743           

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