Documentation: bonding: update miimon default to 100

With commit c1f897ce ("bonding: set default miimon value for non-arp
modes if not set") the miimon default was changed from zero to 100 if
arp_interval is also zero. Document this fact in bonding.rst.

Fixes: c1f897ce ("bonding: set default miimon value for non-arp modes if not set")
Signed-off-by: Jonathan Toppins <jtoppins@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>