addons: bond: add ifname length check in sysfs back up path

addons: bond: add ifname length check in sysfs back up path

When creating a bond, we first use a netlink call, if that
call fails we try to create and setup the bond via sysfs.

If the bond name is longer than 15 chars the netlink call
will fail, we will then enter the sysfs path which creates
the bond by writing to /sys/class/net/bonding_masters. In
this case the bonding driver will simply truncate the bond
name to fit into the 15 chars limit.

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>