ib/ipoib: support multiple devices on the same partition

ib/ipoib: support multiple devices on the same partition

Multiple devices can coexist in a partition provided they have
different scopes.  This patch adds an optional scope argument to
the create_child / delete_child attributes.  Created child devices
are still named the same way as before, so in order to create
multiple child devices in the same partition, an interface name
change will be necessary to make room for subsequent children, eg:

	echo 0xffff 0xe > /sys/class/net/ib0/create_child
	ip link set ib0.ffff name ib0.global

Signed-off-by: Rolf Manderscheid <rvm@obsidianresearch.com>