WFD: Add support for sending Wi-Fi Display service discovery requests

WFD: Add support for sending Wi-Fi Display service discovery requests

wpa_cli p2p_serv_disc_req command can now be used to request WSD
request to be sent to specified or all peers who support WSD.

format: wifi-display <list of roles> <list of subelements>
examples:
p2p_serv_disc_req 00:00:00:00:00:00 wifi-display [source] 2,3,4,5
p2p_serv_disc_req 02:01:02:03:04:05 wifi-display [pri-sink] 3
p2p_serv_disc_req 00:00:00:00:00:00 wifi-display [sec-source] 2
p2p_serv_disc_req 00:00:00:00:00:00 wifi-display [source+sink] 2,3,4,5
p2p_serv_disc_req 00:00:00:00:00:00 wifi-display [source][pri-sink] 2,3,4,5

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