iwlwifi: mvm: set default new STA as non-aggregated

When sending the first ADD_STA HCMD for a STA, the %add_modify
field indicates an addition of a STA and not a modification
of one. In such a case, all fields of the HCMD are used to
initialize the corresponding fields in the FW, regardless of
what bits are set in %modify_mask.

Set the %tid_disable_tx field to mvm_sta->tid_disable_agg in
iwl_mvm_sta_send_to_fw(). If the STA is only updated this will
have no effect, but if it is added - it will make sure the
STA starts with the correct queues - if any - configured as
non-aggregated by default (until told otherwise).

Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>