[Proposal] Replace log trace strings to easily readable

[r4f4ss]

Rationale

Geth use short, intuitive and easy to read and recognise log trace messges like:

>> PING/V5
<< PONG/V5
<< PING/V5
>> PONG/V5

When the log refer to DiskV5 Shisui also inherit those logs from geth, but logs specifically to portal wire protocol have messages non intuitive and hard to read and recognise:

Received ping response
Received pong response

Proposal

This issue propose to substitute the following strings in file portal_protocol.go in order to facilitate visualization and log analysis:

Current log string	New log string
Sending ping request	>> PING/<NETWORK>
Received ping response	<< PONG/<NETWORK>
Sending find nodes request	>> FIND_NODES/<NETWORK>
Sending find content request	>> FIND_CONTENT/<NETWORK>
Sending offer request	>> OFFER/<NETWORK>
Received accept response	<< ACCEPT/<NETWORK>
Sent content response	>> CONTENT/<NETWORK>
Received content response	<< CONTENT/<NETWORK>
Received content response (ENRS)	<< CONTENT_ENRS/<NETWORK>
Received returned content response	<< CONTENT_CONNECTION_ID/<NETWORK>
Received nodes response	<< NODES/<NETWORK>
Received pong response	<< PONG_RESPONSE/<NETWORK>
received ping request	<< PING/<NETWORK>
received find nodes request	<< FIND_NODES/<NETWORK>
received offer request	<< OFFER/<NETWORK>
Sending pong response	>> PONG/<NETWORK>
Sending nodes response	>> NODES/<NETWORK>
Sending enrs content response	>> CONTENT_ENRS/<NETWORK>
Sending raw content response	>> CONTENT_RAW/<NETWORK>
Sending connection id content response	>> CONTENT_CONNECTION_ID/<NETWORK>
Sending accept response	>> ACCEPT/<NETWORK>
Received offer content response	<< OFFER_CONTENT/<NETWORK>

Where <NETWORK> is one of the networks: history,state,bacon.

[GrapeBaBa]

Really nice proposal