em/emx: Fix attach error handling and media leakage in detach

- Add missing ether_ifdetach() if reset fails.
  Reported-by: Johannes Hofmann <Johannes.Hofmann@gmx.de>

- Call ifmedia_removeall() on detach path, since these drivers add
  ifmedia themselves; move ifmedia_init() to the beginning of attach
  for this to work.
em/emx: On attach path, perform another reset if the first one fails

The second reset fixes the 82573L attaching failure.

Reported-and-Tested-by: Johannes Hofmann <Johannes.Hofmann@gmx.de>
kmalloc.9: Add kmalloc_raise_limit to NAME section
kmalloc.9: Mention M_NULLOK in RETURN VALUE section