Add support for sendmmsg/recvmmsg #1010

Job	Run time
Test (stable)	20s
Test (1.63.0)	3m 7s
Rustfmt	12s
Check (armv7-sony-vita-newlibeabihf)	34s
Test (beta)	25s
Check (i686-unknown-hurd-gnu)	34s
Test (nightly)	22s
Clippy	14s
Test (macos)	41s
Check (aarch64-apple-ios)	17s
Test (windows)	1m 15s
Check (aarch64-linux-android)	15s
Docs (armv7-sony-vita-newlibeabihf)	27s
Check (x86_64-apple-darwin)	18s
Docs (aarch64-apple-ios)	12s
Docs (i686-unknown-hurd-gnu)	28s
Check (x86_64-unknown-fuchsia)	15s
Docs (aarch64-linux-android)	13s
Check (x86_64-pc-windows-msvc)	18s
Docs (x86_64-apple-darwin)	16s
Check (x86_64-pc-solaris)	16s
Docs (x86_64-unknown-fuchsia)	15s
Check (x86_64-unknown-freebsd)	17s
Docs (x86_64-pc-windows-msvc)	15s
Check (x86_64-unknown-illumos)	15s
Docs (x86_64-pc-solaris)	13s
Check (x86_64-unknown-linux-gnu)	15s
Docs (x86_64-unknown-freebsd)	15s
Check (x86_64-unknown-linux-musl)	16s
Docs (x86_64-unknown-illumos)	12s
Check (x86_64-unknown-netbsd)	13s
Docs (x86_64-unknown-linux-gnu)	12s
Check (x86_64-unknown-redox)	18s
Docs (x86_64-unknown-linux-musl)	16s
Check (armv7-linux-androideabi)	14s
Docs (x86_64-unknown-netbsd)	12s
Check (i686-linux-android)	14s
Docs (x86_64-unknown-redox)	13s
Docs (armv7-linux-androideabi)	13s
Docs (i686-linux-android)	16s
	15m 33s

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