libertas: simplify and clean up association/start/join setup

Some of the parameters for association/join/start commands aren't
used (like the FH and CF IEs for IBSS, and the FH IE for BSS), so
get rid of their unions to reduce indirection.  Also clean up
structure names for kernel style.

Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>