net: Properly handle pkt IPv4 broadcast destination address

If we receive an IPv4 that has broadcast destination address, then
properly handle it.
This means that for
  * ICMPv4, if CONFIG_NET_ICMPV4_ACCEPT_BROADCAST is set (this is the
    default value) and we receive echo-request then accept the packet.
    Drop other ICMPv4 packets.
  * TCP, drop the packet
  * UDP, accept the packet if the destination address is the broadcast
    address 255.255.255.255 or the subnet broadcast address.
    Drop the packet if the packets broadcast address is not in our
    configured subnet.

In sending side, make sure that we do not route broadcast address
IPv4 packets back to us. Also set Ethernet MAC destination address
properly if destination IPv4 address is broadcast one.

Fixes #10780

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>