Add ipset package to Docker images for custom routing support

[AYastrebov]

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:
Added the ipset package to both Dockerfile and Dockerfile.aarch64. This change is required for custom routing setups in my use case.

Benefits of this PR and context:
ipset enables advanced rule-based routing and network management inside the container, which is necessary for custom routing scenarios.

How Has This Been Tested?
The images were built locally and verified to include ipset. Custom routing functionality was tested and confirmed to work as expected.

Source / References:
https://linux.die.net/man/8/ipset

[github-actions]

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[LinuxServer-CI]

I am a bot, here is the pushed image/manifest for this PR:

ghcr.io/linuxserver/lspipepr-wireguard:1.0.20250521-r0-pkg-95d92213-dev-820cf682bb81057c7fc10dab7f5d922bf5682935-pr-393

[LinuxServer-CI]

I am a bot, here is the pushed image/manifest for this PR:

ghcr.io/linuxserver/lspipepr-wireguard:1.0.20250521-r0-pkg-6bade7b8-dev-acda6267f5742663160ed92b70d6147cc9dd9a47-pr-393

[LinuxServer-CI]

I am a bot, here is the pushed image/manifest for this PR:

ghcr.io/linuxserver/lspipepr-wireguard:1.0.20250521-r0-pkg-88868e8c-dev-7a768405910c873606ab22699f88ea864c15636b-pr-393

[LinuxServer-CI]

I am a bot, here is the pushed image/manifest for this PR:

ghcr.io/linuxserver/lspipepr-wireguard:1.0.20250521-r0-pkg-48221c48-dev-994bbc182b66f1ce35f3526c26f2f570950c591a-pr-393

[drizuid]

you're the only user to ever request this, therefore i believe the universal install docker mod is the better suited solution to your need. that will allow you to install whatever you want without increasing the size, arbitrarily, for everyone else.