ieee1394: eth1394: Move common recv_init code to helper function

There is some common code between ether1394_open and ether1394_add_host
which can be moved to a separate helper function for a slightly smaller
eth1394 driver (-160 bytes on i386.)

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>