Peripheral initiated connection parameter update is ignored

[thomasstenersen]

Describe the bug
If a peripheral initiates a connection parameter update before the first conn param update timer has expired, its requested parameters are ignored (no error code return from bt_conn_le_param_update()). If CONFIG_BT_GAP_AUTO_UPDATE_CONN_PARAMS=n nothing will happen when the timer eventually does expire

To Reproduce
Steps to reproduce the behavior:

1. Checkout thomasstenersen@9a9e240
2. Build and run the peripheral_hr sample (example west build -b nrf5284dk_nrf52840 -d build samples/bluetooth/peripheral_hr)
3. Connect to the peripheral and observe that the first connection parameter update request only comes after >5 seconds.

Expected behavior
I would expect bt_conn_le_param_update() to either

1. Return an error if it is not ready to handle the request yet, or
2. Execute the connection parameter update request as possible.

Logs and console output
nRF Sniffer/Wireshark log: conn-update-delay.zip
Sample log output:

<snip>
Connected
Called conn update
Called conn update
Called conn update
Called conn update
Called conn update
Called conn update
Called conn update
</snip>