luci-app-keepalived: add missing variable declarations

[dannil]

• 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 N/A
• Tested on: (x86/64, 24.10.0-rc4, Firefox) ✅
• ( Preferred ) Mention: @ the original code author for feedback @jempatel
• ( Preferred ) Screenshot or mp4 of changes:
• ( Optional ) Closes: e.g. luci-app-keepalived: scripts broken #7536
• ( Optional ) Depends on: e.g. openwrt/packages#pr-number in sister repo
• Description: (describe the changes proposed in this PR)

Before:

After:

[feckert]

Thanks merged!