luci-mod-network: add speed choices via rpc device status

[sion-111]

This change adds a speed selection field to device settings in LuCI.

Available speeds are populated dynamically using network.device status
via RPC, while still allowing manual custom values to be entered.

ACL permissions were extended to allow read-only access to
network.device status.

Tested on Banana Pi BPI-R4.

• This PR is not from my main or master branch, but a separate branch
• Each commit has a valid Signed-off-by: sion-111 <s.piotrowski91@gmail.com>
• Each commit and PR title has a valid <package name>: title first line subject
• Incremented any PKG_VERSION in the Makefile (not applicable)
• Tested on: Banana Pi BPI-R4
• Screenshot or mp4 of changes

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