Stability fix, keepalive disconnection

[brentru]

WipperSnapper devices are being disconnected/reconnected every ~120000ms.

This is due to two issues fixed by this PR:

1. Rigid timing requirement around the MQTT KeepAlive time (exactly every KAT interval)
2. Blinking the status LED every STATUS_LED_KAT_BLINK_TIMEms causes a blocking behavior that exceeds the client's configured MQTT KeepAlive time, causing the next PINGREQ to execute out-of-bounds

Pre-PR Behavior, note the delta of 6.019 seconds between pings caused by the status LED blinking.

14:37:07.902 -> [235985][V][ssl_client.cpp:369] send_ssl_data(): Writing HTTP request with 2 bytes...
14:37:11.952 -> PING!
14:37:11.952 -> [240019][V][ssl_client.cpp:369] send_ssl_data(): Writing HTTP request with 2 bytes...
14:37:14.963 -> Blinking status LED STATUS_LED_KAT_BLINK_TIME
14:37:17.971 -> PING!
14:37:17.971 -> [246044][V][ssl_client.cpp:369] send_ssl_data(): Writing HTTP request with 2 bytes...
14:37:17.971 -> [246058][V][ssl_client.cpp:324] stop_ssl_socket(): Cleaning SSL connection.
14:37:18.004 -> FSM_NET_ESTABLISH_MQTT

Post-PR behavior

15:13:06.583 -> [962488][V][ssl_client.cpp:369] send_ssl_data(): Writing HTTP request with 2 bytes...
15:13:06.999 -> Blinking status LED STATUS_LED_KAT_BLINK_TIME
15:13:10.609 -> PING!
15:13:10.609 -> [966523][V][ssl_client.cpp:369] send_ssl_data(): Writing HTTP request with 2 bytes...
15:13:14.647 -> PING!

This pull request:

• Shortens the execution time of statusLEDBlink()
• Loosens timing requirement within pingBroker()

[lorennorman]

looks perfect! 💯