MF11 r331330: Fix kernel memory disclosure in svr4_sys_getdents64

svr4_sys_getdents64() copies a dirent structure to userland. When
calculating the record length for any given dirent entry alignment is
performed. However, the aligned bytes are not cleared, this will
trigger an info leak.

Reported by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Security: Kernel memory disclosure (801)
Sponsored by: The FreeBSD Foundation