qemu: Update to version 8.1.1 and add libslirp for net user backend

qemu: Update to version 8.1.1 and add libslirp for net user backend

- Update from version 8.0.3 to 8.1.1
- In CU179 the update of qemu caused at least one user to have a problem starting his
   qemu system as the qemu bundled slirp library used for the net user backend was removed
   in version 7.2. Unfortunately no user tested qemu in the CU179 Testing phase, or if they
   did they are not using the net user backend.
- This patch adds the --enable-slirp option to configure and installs libslirp in a
   separate patch.
- I can't test if this now works as I don't use qemu anywhere.
- Changelog is too large to include here.
    8.1
	https://wiki.qemu.org/ChangeLog/8.1

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>