MFC r332042: Fix kernel memory disclosure in linux_ioctl_socket

MFC r332042: Fix kernel memory disclosure in linux_ioctl_socket

strlcpy is used to copy a string into a buffer to be copied to userland,
previously leaving uninitialized data after the terminating NUL.  Zero
the buffer first to avoid a kernel memory disclosure.

admbugs:	765, 811
Reported by:	Ilja Van Sprundel <ivansprundel@ioactive.com>
Reported by:	Vlad Tsyrklevich
Sponsored by:	The FreeBSD Foundation

git-svn-id: svn://svn.freebsd.org/base/stable/10@332064 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f