deltaq tracing improvements

[karknu]

The review of #1255 left some comments unaddressed.

• [ ] Tracing https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r348657233 https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r349025487 https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r349027464
• [ ] Unpack https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r348990198
• [ ] Superfluous $! https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r349001924 https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r349020112
• [ ] Haddock https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r349002868 https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r349015425
• [ ] Grammar, spelling https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r349007941 https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r349008291 https://github.com/input-output-hk/ouroboros-network/pull/1255#discussion_r349008774