Some APs transmit AMPDU and MPDU by turns. Moreover, the sequence
numbers of AMPDU and MPDU are out of order, e.g. MPDU(1253) -
AMPDU(1251, 1252) - MPDU(1254) - AMPDU(1255, 1256). In order to
receive both AMPDU and MPDU in order, MPDU must be reordered with
AMPDU.
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