sysvipc: Fix compat msgctl (BZ#24570)

The __IPC64 flags is meant to be used to enable the new sysv struct
format when the architectures supports it (ARCH_WANT_IPC_PARSE_VERSION
config flag on Linux kernel).

This currently issue only affects alpha.

	[BZ #24570]
	* sysdeps/unix/sysv/linux/msgctl.c (__old_msgctl): Remove __IPC_64
	usage.