[1.0.4] P2P: Fix sync stuck corner case

[heifner]

Update chain_info on accepted_block signal since chain_head has changed. The sync logic needs up to date info of the state of the node. This normally doesn't cause an issue because under normal conditions the node would soon receive a accepted_block_header or irreversible_block signal which would update the net_plugin state.

Resolves #998

[ericpassmore]

Note:start
category: System Stability
component: P2P
summary: Fix sync stuck that can occur with very tight sync-fetch-span.
Note:end