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Add the 3com 3C507 card to the if_ie.c driver. The files elink.c and
elink.h are helding routines that are shared between the 3C507 and the
3C509/3C579. if_ie507.h are constant declarations unique to the 3C507.
The code is based on the NetBSD driver if_ie.c donated to NetBSD by
Rafal Boni and then modified by Charles Hannum.
