net/appletalk: Fix kernel memory disclosure

[ Upstream commit ce7e40c432ba84da104438f6799d460a4cad41bc ]

ipddp_route structs contain alignment padding so kernel heap memory
is leaked when they are copied to user space in
ipddp_ioctl(SIOCFINDIPDDPRT). Change kmalloc() to kzalloc() to clear
that memory.

Signed-off-by: Vlad Tsyrklevich <vlad@tsyrklevich.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>