From https://github.com/rootless-containers/slirp4netns/blob/4889f5299f407d7d7566c76a3b8b5f71c99b6db5/qemu_patches/0002-slirp-allow-custom-MTU.patch

Original commits:
* https://github.com/rootless-containers/slirp4netns/commit/ea630a7e945cf538184ff1b1b4bd7b8ddc01993e
* https://github.com/rootless-containers/slirp4netns/commit/1508a66c93c223555f08651592dde3d2d708b166
* https://github.com/rootless-containers/slirp4netns/commit/19f3f41df4066d6103e6f882500e24db7ea7d9e1
* https://github.com/rootless-containers/slirp4netns/commit/a11abedafcc627ef0657999e63b211b0f26d4c02
* https://github.com/rootless-containers/slirp4netns/commit/2adbd7c449944d3b837164c86eedd3dcabbba1a6



Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>