delete copy preamble from ppdu_desc to peer in data type case.
this will give mu_bar preamble of a data frame instead of ctrl frame.
this will not affect tx_capture given that preamble is copied to
phy_type in ppdu_desc from ppdu_desc preamble itself.
this should fix issue with pulling information from ppdu descriptor by
having data frames with low mcs. mcs was correct but preamble gave
impression that frame was a data but it was a ctrl frame.
Change-Id: Id82e6eb98af0e9488227bff43fc77f188eee77e3