Auto merge of #916 - LuoZijun:patch-1, r=alexcrichton

Add `IFF_*` constants  to linux, android and fuchsia

Add constants to android and fuchsia:

*    IFF_TUN
*    IFF_TAP
*    IFF_NO_PI

Type problem: https://github.com/rust-lang/libc/issues/915

so change constants type `libc::c_short` to `libc::c_int` :

*    IFF_*