Add `ip_mtu` and `ipv6_mtu` on linux platform (#1320) #4829

Job	Run time
Check selected Tier 3 platforms (nightly)	5m 35s
Check nightly-only targets (nightly)	20s
Check (stable)	6m 23s
Check (nightly)	6m 15s
Check --no-default-features (nightly)	55s
Check (1.63)	10m 55s
Rustfmt	6s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 7s
Test rustix_use_experimental_asm (s390x-linux)	1m 21s
Test (ubuntu)	41s
Test use-libc (ubuntu)	40s
Test (ubuntu-20.04)	44s
Test use-libc (i686-linux)	1m 20s
Test (i686-linux)	1m 17s
Test use-libc (aarch64-linux)	1m 11s
Test (aarch64-linux)	1m 15s
Test use-libc (powerpc64le-linux)	1m 10s
Test (powerpc64le-linux)	1m 6s
Test use-libc (riscv64-linux)	1m 25s
Test (riscv64-linux)	1m 14s
Test use-libc (s390x-linux)	1m 8s
Test (s390x-linux)	1m 14s
Test use-libc (arm-linux)	1m 12s
Test (arm-linux)	1m 6s
Test (ubuntu-stable)	37s
Test (i686-linux-stable)	1m 1s
Test (aarch64-linux-stable)	1m 6s
Test (riscv64-linux-stable)	1m 5s
Test (s390x-linux-stable)	1m 9s
Test (powerpc64le-linux-stable)	1m 4s
Test (arm-linux-stable)	1m 12s
Test (ubuntu-1.63)	2m 51s
Test (i686-linux-1.63)	3m 36s
Test (aarch64-linux-1.63)	3m 24s
Test (riscv64-linux-1.63)	3m 36s
Test (s390x-linux-1.63)	3m 16s
Test (powerpc64le-linux-1.63)	3m 22s
Test (arm-linux-1.63)	3m 28s
Test (macos-latest)	41s
Test (macos-13)	1m 11s
Test (windows)	49s
Test (windows-2019)	54s
Test (musl)	43s
	1h 24m 45s

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