Silence constant X is never used warings

[bzEq]

Fix warnings on AIX

warning: constant `IF_NAMESIZE` is never used
   --> src/unix/aix/mod.rs:964:11
    |
964 | pub const IF_NAMESIZE: ::c_int = 16;
    |           ^^^^^^^^^^^
    |
    = note: `#[warn(dead_code)]` on by default

warning: constant `IFNAMSIZ` is never used
   --> src/unix/aix/mod.rs:965:11
    |
965 | pub const IFNAMSIZ: ::c_int = 16;
    |           ^^^^^^^^

warning: constant `ARPOP_REQUEST` is never used
   --> src/unix/aix/mod.rs:988:11
    |
988 | pub const ARPOP_REQUEST: ::c_int = 1;
    |           ^^^^^^^^^^^^^

warning: constant `ARPOP_REPLY` is never used
   --> src/unix/aix/mod.rs:989:11
    |
989 | pub const ARPOP_REPLY: ::c_int = 2;
    |           ^^^^^^^^^^^

These constants have been defined in src/unix/mod.rs and have the same numeric values on AIX.

[rustbot]

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[JohnTitor]

These warnings mean there are duplicate declarations for consts, so you have to remove or separate them (note that we re-export modules from lower to upper).