FWIW I agree with Antoine and Martin: ignoring EBADF is a bad idea,
quite dangerous.
The man page probably says this to highlight that users shouldn't
*retry* close():
"""
       Retrying the close() after a failure return is the wrong thing to do,
       since this may cause a reused file descriptor from another thread to
       be closed.  This can occur because the Linux kernel always releases
       the file descriptor early in the close operation, freeing it for
       reuse; the steps that may return an error, such as flushing data to
       the filesystem or device, occur only later in the close operation.

"""

(Including on EINTR).

In short, I think that the change is a good idea: Socket.close() is
guaranteed to be idempotent, so this error can only happen in case of
invalid usage.