The rime channel header size is now stored in uint16_t.

If using an 8 byte rime address size in the multihop example,
an 261 bit header is created. This produced an overflow.
Merge branch 'rime_channel_hdrsize_overflow' into tests-stm32w
Set local rime addresses for my hardware.
[STM32W] Set PACKETBUF_CONF_HDR_SIZE to 56 byte to fix multihop for 8 byte rime addresses.
Merge branch 'stm32w_example_multihop_fix' into tests-stm32w