test: use default address type (bech32) for wallet_bumpfee tests
test: use default address type (bech32) for wallet_bumpfee tests

The use of native segwit addresses (pure p2wpkh instead of p2sh-p2wpkh) leads
to smaller transaction sizes, needing adaption of some constants in the
following test cases:
    - test_dust_to_fee(): adaption of dust calculation
          (p2wpkh spend estimate of 67 is taken from src/policy/policy.cpp:GetDustThreshold())
    - test_maxtxfee_fails(): lowering -maxtxfee setting to trigger fail

DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin,peercoin/peercoin,peercoin/peercoin,peercoin/peercoin,peercoin/peercoin