Missing support for `sockaddr_vm`'s `svm_flags`

[james-callahan]

sockaddr_vm is currently missing the svm_flags field. See https://lkml.org/lkml/2020/12/11/249

The structure is defined at

libc/src/unix/linux_like/linux/mod.rs

Lines 507 to 513 in b4686c6

	pub struct sockaddr_vm {
	pub svm_family: ::sa_family_t,
	pub svm_reserved1: ::c_ushort,
	pub svm_port: ::c_uint,
	pub svm_cid: ::c_uint,
	pub svm_zero: [u8; 4]
	}

See also rust-vsock/vsock-rs#29