OWE: PTK derivation workaround in STA mode

OWE: PTK derivation workaround in STA mode

Initial OWE implementation used SHA256 when deriving the PTK for all OWE
groups. This was supposed to change to SHA384 for group 20 and SHA512
for group 21. The new owe_ptk_workaround=1 network parameter can be used
to enable older behavior mainly for testing purposes. There is no impact
to group 19 behavior, but if enabled, this will make group 20 and 21
cases use SHA256-based PTK derivation which will not work with the
updated OWE implementation on the AP side.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>