luci-mod-system: add LED speed and duplex triggers

[abajk]

Many devices have LEDs to signal a specific link speed. They are incorrectly displayed in LUCI when they are defined. This commit adds the missing speed and duplex triggers.

Tested on: mediatek/filogic/ex5601, snapshot, Firefox

• This PR is not from my main or master branch 💩, but a separate branch ✅
• Each commit has a valid ✒️ Signed-off-by: <my@email.address> row (via git commit --signoff)
• Each commit and PR title has a valid 📝 <package name>: title first line subject for packages
• Incremented 🆙 any PKG_VERSION in the Makefile
• Tested on: (architecture, openwrt version, browser) ✅
• ( Preferred ) Mention: @feckert the original code author for feedback
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• Description: (describe the changes proposed in this PR)