iwlwifi: move an ieee80211_get_tid() call

Introduce a local change. It seems ieee80211_get_tid() does not deal
with non-dataqos packets unlike net80211's ieee80211_gettid().
Gernally all calls in Linux drivers to ieee80211_get_tid() seem to
be proceeded by an ieee80211_is_data_qos() check.

Moving the ieee80211_get_tid() has no difference in the result, but
(a) saves us the call if we do not need it due to an earlier return,
and (b) allows us to put an assert into the LinuxKPI ieee80211_get_tid()
implementation to avoid accidentally returning random frame header data
in case of a missing earlier ieee80211_is_data_qos() check in (future/
other) drivers.

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