Protocol-Test: Remove unnecessary MAX_INV Limit to MAX_MESSAGE test / Or replace.

[jonajosejg]

The following Test found in
https://github.com/bcoin-org/bcash/blob/master/test/protocol-test.js#L151

The GetDataPacket size values to 1800003
Whilst the current updated MAX_MESSAGE value is 2097152

There is a possibility of changing the typeof invitems, or simply removing the test I'd be willing to hear out what is the better option. So that I can replace or remove the check in the test file for ci purposes.