bonding: fix link recovery in mode 2 when updelay is nonzero

Before this change when a bond in mode 2 lost link, all of its slaves
lost link, the bonding device would never recover even after the
expiration of updelay. This change removes the updelay when the bond
currently has no usable links. Conforming to bonding.txt section 13.1
paragraph 4.

Fixes: 41f89100 ("bonding: ignore updelay param when there is no active slave")
Signed-off-by: Jonathan Toppins <jtoppins@redhat.com>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>