[1.0.2] P2P: Allow irreversible mode syncing to continue when LIB is paused

[heifner]

• Allow a node to continue syncing ahead when LIB is paused. This is important when running in irreversible mode as the chain_head does not advance until LIB advances.
• Added some additional debug logging to net_plugin. Also added an info level log when it allows a node to sync ahead past sync-fetch-span of head because LIB is paused.
• Add new test cases for startup-catchup test.
  • Sync with a sync-fetch-span of 1 while in irreversible mode.
    • Note this only tripped the issue in Savanna mode as the test doesn't run long enough to trigger a LIB catchup in legacy mode. It does a HEAD catchup in legacy mode (at least in my local testing). I didn't modify the test to produce more blocks to force a LIB catchup in legacy mode as the test does already trigger LIB catchup in Savanna mode.

Tested syncing Kylin past the large LIB pause.

Resolves #773

[ericpassmore]

Note:start
category: Other
component: Plugins/Cleos/Utils
summary: P2P: Allow irreversible mode syncing to continue when LIB is paused.
Note:end

[greg7mdp]

Suggested change

	if (blk_num < head_num) { // avoid underflow on blk_num - head_num
	return true;
	}
	block_num_type num_blocks_not_applied = blk_num - head_num;
	block_num_type num_blocks_not_applied = blk_num > head_num ? blk_num - head_num : 0;