[3.13] gh-100218: correctly set `errno` when `socket.if_{nametoindex,indextoname}` raise `OSError` (GH-140905) (#141285)

Previously, socket.if_nametoindex() and socket.if_indextoname() could raise
an `OSError` with a `None` errno. Now, the errno from libc is propagated.

(cherry picked from commit 3ce2d57b2f02030353af314d89c5f6215d2f5c96)