When debugging multihop wireless network, it is useful to emulate non-transitive
network, that is, node A can communicate with B and B can communicate with C,
but A cannot communicate with C directly.
If `XBEE_DENIED_ADDRESSES`, which is an array of XBee long addresses, is
defined, packets from those addresses are dropped silently.
Example:
CFLAGS += "-DXBEE_DENIED_ADDRESSES={ 0x02, 0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0x02, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11 }"
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