[cashtab-faucet] Tighten IP rules

Summary:
Seeing an uptick in faucet abuse after reducing required score and reducing IP rate limits.

Put IP rate limits back to previous settings.

Ultimately we will need a more effective captcha here, and this is in the works, but want to see if this tweak has any impact.

Test Plan: npm test

Reviewers: #bitcoin_abc, alitayin

Reviewed By: alitayin

Differential Revision: https://reviews.bitcoinabc.org/D18431