tests: Wait before initiating DPP from thread in sigma_dut testing

tests: Wait before initiating DPP from thread in sigma_dut testing

Starting a thread to initiate DPP before starting the responder through
sigma_dut can result in unexpected testing behavior since there may not
be enough time to get the responder enabled before timing out som
initiator actions. Wait a second at the beginning of the initiator
thread in dpp_init_conf() similarly to how this was handled in other
initiator-from-thread cases.

Signed-off-by: Jouni Malinen <j@w1.fi>