FT: Remove optional fields from RSNE when using PMF

FT: Remove optional fields from RSNE when using PMF

The PMKIDCount, PMKID List, and Group Management Cipher Suite fields are
optional to include in the RSNE in cases where these would not have
values that are different from the default values. In practice,
PMKIDCount is always 0 in Beacon and Probe Response frames, so the only
field of these that could have a non-default value is Group Management
Cipher Suite. When BIP is used, that field is not needed either due to
BIP being the default cipher when PMF is enabled.

Remove these fields from RSNE when BIP is used to save six octets in
Beacon and Probe Response frames. In addition to reduced frame length,
this is a workaround for interoperability issues with iOS 8.4 in cases
where FT and PMF are enabled. iOS seems to be rejecting EAPOL-Key msg
3/4 during FT initial mobility domain association if the RSNE includes
the PMKIDCount field.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>