Documentation update for MAC access restrictions.

With change ag/73407247, the device's P2P MAC adress will only be
available to callers holding the LOCAL_MAC_ADDRESS permission, and will
be anonymized otherwise. This CL updates the documentation in
WifiP2pManager to reflect that.

Bug: 132055766
Test: atest tests/src/android/net/wifi/

Change-Id: I9c2b5ce2cb2c2d2d6766fd34f3451ad4f22a5698