[3.1 -> 3.2] net_plugin improve block latency calculation

[heifner]

Remove the +1 to the block latency calculation otherwise even 0ms latency indicates 1 block latency instead of 0. The +1 makes the comparisons of head and msg.head in the if-else off by 1 when there is no latency.

Added additional logging so that issues like #588 are easier to debug.

Before:

debug 2022-12-21T21:54:29.938 net-3     net_plugin.cpp:1790           recv_handshake       ] ["localhost:9878 - f9bdaf6" - 43 127.0.0.1:52370] Network latency is 0ms, 0 blocks discrepancy by network latency, 1 blocks discrepancy expected once message received

After:

debug 2023-01-31T00:27:27.386 net-0     net_plugin.cpp:1795           recv_handshake       ] ["localhost:9878 - 978ab39" - 1 127.0.0.1:54362] Network latency is 0ms, 0 blocks discrepancy by network latency, 0 blocks discrepancy expected once message received

Merges release/3.1 into release/3.2 including #676