comms/ebusd: update to v21.1

Bug Fixes

• fix for publishing several MQTT updates at once
• optimized keep alive option for net devices
• fix for duplicate entry "minarbitrationmicros" in HTTP GET
• fix for extra send retry
• fix for newer compiler versions
• fix for potential illegal string usages
• fix for named net device not being resolvable during startup

Features

• added Raspberry Pi docker image
• added support for Cygwin build
• added option to use "\*" as trailing wildcard for circuit and name in MQTT /list topic
• added "--mqttinsecure" option
• updated to newest version of enhanced protocol
• added adapter 3 PIC tool "ebuspicloader" for uploading new firmware and configuring fix IP address

Approved by: krion
Differential Revision: https://reviews.freebsd.org/D28112