HTLC Claim TX being rejected for too low of feerate

[niftynei]

Issue and Steps to Reproduce

Testnet node's logs are being filled with spam from a channel that's failing to spend an HTLC output on an 'illegally closed' channel. (Peer tried to cheat).

"id": "02fd753c8ad77d2601637b6add4362fec59f4d3e8190347ab4d155f3e9a76e113c",
    ...
          "our_to_self_delay": 144,
          "max_accepted_htlcs": 483,
          "status": [
            "ONCHAIN:Tracking their illegal close: taking all funds",
            "ONCHAIN:1 outputs unresolved: waiting confirmation that we spent THEIR_HTLC (6aeb328adfe44029183c06a280f5fb064f9c1b251b6d59dbb71612a713ef51c1:0) using THEIR_HTLC_FULFILL_TO_US"
          ],
...
          "htlcs": [
            {
              "direction": "in",
              "id": 72,
              "msatoshi": 8888888,
              "amount_msat": "8888888msat",
              "expiry": 1478044,
              "payment_hash": "8cdeafca09f4b3c1b91179996a1f59bbce4e77c952e9e000b21d7891616945a8",
              "state": "RCVD_REMOVE_REVOCATION"
            }
          ]
        }
      ]

The problem seems to be that the feerate on the HTLC claiming transaction is too low.

2019-04-04T18:07:55.447Z lightningd(3774617): Broadcasting tx 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: 26 error code: -26?error message:?min relay fee not met, 136 < 143 (code 66)?

Transaction to be spent from: https://blockstream.info/testnet/tx/6aeb328adfe44029183c06a280f5fb064f9c1b251b6d59dbb71612a713ef51c1?expand

Reported-By: @nitramiz