fix(ethernet): _make_data turns MAC addresses into ASCII hex text #1123

Describe the bug
Ethernet._make_data returns MAC addresses in a form that make() packs as ASCII text. An all-zero MAC comes back as the bytes of '000000000000', so Ethernet.from_data(e.info), and any Frame wrapping Ethernet, does not rebuild byte for byte.

Reproduction
Build an Ethernet frame with an all-zero MAC, then rebuild it with from_data. Reported by the #1115 worker; re-verify on main first.

Expected behavior
from_data round-trips the MAC addresses byte for byte.

System information
main at bdba4fb9d, CPython 3.14.7, Linux.

Additional context
Found by the #1090–#1102 wave's audit and cross-reviews.