eigrpd: Start fixing eigrp_interface

eigrpd: Start fixing eigrp_interface

The EIGRP interface handling code created 2 levels
of interface information, the ei( created per *connected*
address?????) and the ifp->info pointer.

Start the combination of pushing these together and
cleaning up the weirdness that is these two data
structures.

This commit probably breaks eigrp's handling of
interfaces.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>