vswitch: More accurately identify slave status for compatibility

vswitch: More accurately identify slave status for compatibility

Ben Pfaff dug through the kernel sources and reported that
bond_miimon_inspect() supports four BOND_LINK_* states:

       * BOND_LINK_UP: carrier detected, updelay has passed.

       * BOND_LINK_FAIL: carrier lost, downdelay in progress.

       * BOND_LINK_DOWN: carrier lost, downdelay has passed.

       * BOND_LINK_BACK: carrier detected, updelay in progress.

And that bond_info_show_slave() only considers BOND_LINK_UP to be "up"
and anything else to be "down".

Thanks for doing this and suggesting a fix, Ben!