Simplify supported rates and BSS membership selectors generation

Simplify supported rates and BSS membership selectors generation

Use a common helper function to generate the complete list of supported
rates and BSS membership selectors so that building the Supported Rates
and BSS Membership Selectors and the Extended Supported Rates and BSS
Membersip Selectors elements can be generated without having to
duplicate the logic for determining the actual values for the
rates/selectors. The functions for building these elements are now
simply selecting the subset of the values from the output from the
helper function.

Signed-off-by: Jouni Malinen <quic_jouni@quicinc.com>