If a DSA switch driver cannot program an ageing time value due to it
being out-of-range, switchdev will raise a stack trace before failing.

To fix this, add ageing_time_min and ageing_time_max members to the
dsa_switch in order for the switch drivers to optionally specify their
supported ageing time limits.

The DSA core will now check for provided ageing time limits and return
-ERANGE from the switchdev prepare phase if the value is out-of-range.
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>