[backport] - Adjust ATX limit to 1_500_000

[pigmej]

Backport of #5512 to v1.3

[codecov]

Codecov Report

Attention: 45 lines in your changes are missing coverage. Please review.

Comparison is base (15b54b2) 77.3% compared to head (2a7650d) 77.3%.
Report is 6 commits behind head on v1.3.

Files	Patch %	Lines
p2p/server/server.go	44.1%	37 Missing and 1 partial ⚠️
p2p/server/deadline_adjuster.go	96.7%	2 Missing and 1 partial ⚠️
p2p/dhtdiscovery/discovery.go	93.9%	2 Missing ⚠️
fetch/fetch.go	66.6%	0 Missing and 1 partial ⚠️
node/node.go	83.3%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##            v1.3   #5516    +/-   ##
======================================
  Coverage   77.3%   77.3%            
======================================
  Files        260     261     +1     
  Lines      30659   30861   +202     
======================================
+ Hits       23711   23877   +166     
- Misses      5451    5486    +35     
- Partials    1497    1498     +1     

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