iwlwifi: set correct single/dual stream mask

Even the initial single/dual stream values will be overridden later when
issue link quality command; but still make sense not to use hard-code
value during initialization. Single/Dual stream mask are used to indicate the
best antenna for SISO/MIMO; different NIC has different tx antenna
configuration; so the parameter need to based on the valid tx antenna.

1x2 device: single tx antenna available, only SISO is valid
configuration, but still need to set up MIMO configuration, so set it up
with antenna A & B as default.
2x2 device: two tx antenna available, dual_stream will use both valid
antenna.

3x3 device: three tx antenna available, skip the first antenna and
choice the second and third antenna for dual_stream.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>