Add support for using random local MAC address

Add support for using random local MAC address

This adds experimental support for wpa_supplicant to assign random local
MAC addresses for both pre-association cases (scan, GAS/ANQP) and for
connections. MAC address policy for each part can be controlled
separately and the connection part can be set per network block.

This requires support from the driver to allow local MAC address to be
changed if random address policy is enabled. It should also be noted
that number of drivers would not support concurrent operations (e.g.,
P2P and station association) with random addresses in use for one or
both.

This functionality can be controlled with the global configuration
parameters mac_addr and preassoc_mac_addr which set the default MAC
address policies for connections and pre-association operations (scan
and GAS/ANQP while not connected). The global rand_addr_lifetime
parameter can be used to set the lifetime of a random MAC address in
seconds (default: 60 seconds). This is used to avoid unnecessarily
frequent MAC address changes since those are likely to result in driver
clearing most of its state. It should be noted that the random MAC
address does not expire during an ESS connection, i.e., this lifetime is
only for the case where the device is disconnected.

The mac_addr parameter can also be set in the network blocks to define
different behavior per network. For example, the global mac_addr=1 and
preassoc_mac_addr=1 settings and mac_addr=0 in a home network profile
would result in behavior where all scanning is performed using a random
MAC address while connections to new networks (e.g.,
Interworking/Hotspot 2.0) would use random address and connections to
the home network would use the permanent MAC address.

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