Add basic packet filtering via APF program.

This includes dropping IPv4 broadcast packets besides DHCP packets
destined to this device, and IPv6 ICMP6 NAs to ff02::1.
Also add optional IPv4 multicast filtering to support
WifiManager.MulticastLock.

Bug: 26238573
Change-Id: I61fd4c3f40db40c4b3ec5ac5999c2d7f0539a589