iwlwifi: mvm: don't hide HE radiotap data in SKB

Hiding the HE radiotap data for further processing of the SKB just
caused another bug when adding the L-SIG data. Simply stop doing
this and adjust the skb->data pointer accordingly when we need to
get the 802.11 header.

While at it, also verify and fix the data alignment, we need to add
2 bytes padding with the vendor data to ensure the whole length of
all radiotap headers is a multiple of 4.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: 6721039d ("iwlwifi: mvm: add L-SIG length to radiotap")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>