Provide network_receive_minimum in RPC/WS active_difficulty

[guilhermelawless]

On mainnet I get the following response:

{
    "multiplier": "1.5",
    "network_current": "fffffffaaaaaaaab",
    "network_minimum": "fffffff800000000",
    "network_receive_current": "fffffff07c1f07c2",
    "network_receive_minimum": "fffffe0000000000"
}

The multiplier between network_receive_minimum and network_receive_current is 33, plugging that into our normalization expression (33 + (64 - 1)) / 64 yields 1.5 as expected.

[PlasmaPower]

How about a network_receive_current too? That seems a bit more useful to me, unless current is inaccurate to the degree where it's better to use minimum anyways, which would be a separate issue.

[guilhermelawless]

@PlasmaPower thanks for the suggestion and for the original suggestion of adding this to the RPC (was already in the works, just waiting for epoch 2 to finish 👍).

The node applies a function to normalize the prioritization with respect to the block type and even the epoch, so that a receive block doesn't have 10x the priority of a send block with less work generated. Essentially this means network_current applies to all blocks with some small margin of error. The normalization function is here: https://github.com/nanocurrency/nano-node/blob/V21.1/nano/lib/work.cpp#L148

[guilhermelawless]

@PlasmaPower thanks for clarifying via DM, indeed it is possible to take advantage of the normalization to still provide less work for receive blocks and obtain the same priority. Added network_receive_current