mcd v2.4

Changes

• New mctl show router-ports command to list multicast router ports grouped
  per bridge, also available as JSON, issue kernelkit/infix#395
• Improve mctl show igmp json multicast-router-ports output; entries are
  now per-bridge objects with bridge and ports keys
• RFC3376 §8.6/§8.7: send a startup query burst when assuming the querier
  role. The querier now sends Robustness Variable General Queries at
  Query Interval / 4 before switching to the normal query cadence, giving
  hosts a much faster initial response, issue #5
• mctl output width now follows the actual terminal width instead of being
  capped at 78 columns; line wrapping is left to the terminal

Fixes

• Fix #4: IGMP queries sent with all-zeroes source MAC when an interface
  appears via netlink after the configuration file has already been parsed.
  The hardware address is now re-fetched on every netlink RTM_NEWLINK event