Update makeseeds.py to support 0.25.x
Update makeseeds.py to support 0.25.x

Summary: Update the user agent filter and minimum block height.

Test Plan:
With the file {F5396240} as test_seeds.dump:
  ./contrib/seeds/makeseeds.py < test_seeds.dump
Should output the 1.1.1.1 and 4.4.4.4 IPs.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D11049

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