FILS: DHCP relay for HLP requests

FILS: DHCP relay for HLP requests

The new dhcp_server configuration parameter can now be used to configure
hostapd to act as a DHCP relay for DHCPDISCOVER messages received as
FILS HLP requests. The dhcp_rapid_commit_proxy=1 parameter can be used
to configure hostapd to convert 4 message DHCP exchange into a 2 message
exchange in case the DHCP server does not support DHCP rapid commit
option.

The fils_hlp_wait_time parameter can be used to set the time hostapd
waits for an HLP response. This matches the dot11HLPWaitTime in IEEE Std
802.11ai-2016.

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