iwlwifi: use IWL_DEFAULT_MAX_TX_POWER for max_eirp

max_eirp affects the txpower configured to the power,
so use the max tx power (22) instead of some other
value.

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>