Update kernel version in syscall-names.list to 4.16.

Linux 4.16 does not add any new syscalls; this patch updates the
version number in syscall-names.list to reflect that it's still
current for 4.16.

Tested for x86_64 (compilation with build-many-glibcs.py, using Linux
4.16).

	* sysdeps/unix/sysv/linux/syscall-names.list: Update kernel
	version to 4.16.