policy: relax dust thrashold to 1000 dewies/kB, which aligns to lbrycrd

[roylee17]

An output is considered dust if the cost to the network to spend the coins is more than 1/3 of the minimum free transaction relay fee, which has a default rate of 1000 satoshis/kb

bitcoind refactored dust threshold calculation, which removed the multiply factor of 3 from the code, but increased the DUST_RELAY_TX_FEE from 1000 to 3000 (satoshi/kb).

lbrycrd adopted the refactored code but also kept the rate to 1000 dewies/kB, which means:

An output is considered dust if the cost to the network to spend the
coins is more than the minimum free transaction relay fee.

This commit updates lbcd to align the policy.

[roylee17]

Reference:

• https://github.com/bitcoin/bitcoin/commit/b1385852ef2ba45fd6926d75497646debf79e686
• https://github.com/lbryio/lbrycrd/commit/4da4ab1995945fc0b739927bcd0dbe9638285e41

[roylee17]

Fix #89

[coveralls]

Pull Request Test Coverage Report for Build 2975325203

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 9 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.01%) to 51.653%

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Files with Coverage Reduction	New Missed Lines	%
mempool/mempool.go	1	65.36%
peer/peer.go	8	76.31%
<!--	Total:	9		-->

Totals
Change from base Build 2968257507:	0.01%
Covered Lines:	22486
Relevant Lines:	43533

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💛 - Coveralls