Add setter and getter for `multicast_ifv4` and `multicast_ifv6` #4729

Job	Run time
Check nightly-only targets (nightly)	23s
Check selected Tier 3 platforms (nightly)	2m 47s
Check (stable)	3m 14s
Check --no-default-features (nightly)	57s
Check (nightly)	3m 2s
Rustfmt	13s
Check (1.63)	3m 13s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 10s
Test rustix_use_experimental_asm (s390x-linux)	1m 16s
Test (ubuntu)	35s
Test use-libc (ubuntu)	39s
Test (ubuntu-20.04)	36s
Test use-libc (i686-linux)	1m 19s
Test (i686-linux)	37s
Test use-libc (aarch64-linux)	1m 27s
Test (aarch64-linux)	38s
Test use-libc (powerpc64le-linux)	1m 11s
Test (powerpc64le-linux)	36s
Test use-libc (riscv64-linux)	1m 3s
Test (riscv64-linux)	36s
Test use-libc (s390x-linux)	1m 6s
Test (s390x-linux)	36s
Test use-libc (arm-linux)	1m 5s
Test (arm-linux)	37s
Test (ubuntu-stable)	35s
Test (i686-linux-stable)	35s
Test (aarch64-linux-stable)	37s
Test (riscv64-linux-stable)	35s
Test (s390x-linux-stable)	31s
Test (powerpc64le-linux-stable)	36s
Test (arm-linux-stable)	37s
Test (ubuntu-1.63)	35s
Test (i686-linux-1.63)	35s
Test (aarch64-linux-1.63)	36s
Test (riscv64-linux-1.63)	34s
Test (s390x-linux-1.63)	32s
Test (powerpc64le-linux-1.63)	37s
Test (arm-linux-1.63)	38s
Test (macos-latest)	22s
Test (macos-13)	37s
Test (windows)	30s
Test (windows-2019)	22s
Test (musl)	37s
	39m 37s

Provide feedback