Fix coap_str_hash macro

coap_str_hash called coap_hash() with wrong parameter ordering.
bugfix: Block1 handling broken

This change contains a quick and dirty workaround for the following
bug that has been reported by Andrea Azzarà:

  "When sending a file with a POST to a CoAP server, such as

  ./coap-client -m post coap://vs0.inf.ethz.ch:5683/large-create/ -b 64
  -t 0 -f test

  the M bit is not correctly set to 1."
Merge commit 'bb9b01224212aa8e72032e397bfec762fcef8eea'

This merge fixes the bug in coap_str_hash() macro.