wifi: ieee80211: use default for medium synchronization delay

Default values are defined for the information included in the Medium
Synchronization Delay Information subfield. The spec says to
initialize the values to these defaults and only change them when
included.

Return the default value instead of zero so that the defaults are
used when the field is not included in the association response.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230618214435.a7725bef3795.I2d3528cf4af021c5b37f97fbe64ae9116ce9bef1@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>