Extract the FCS decoding section of the PPP_HDLC dissector to
allow the CHDLC dissector to use the same routine.
The ppp_options used for preferences has been renamed to
fcs_options and exported via packet-ppp.h so CHDLC gets a
separate (but identical) FCS preference.
This means prefs.h has to be included before packet-ppp.h so a
couple of ppp related files (packet-{gtp,null,raw,vj}.c) had
their includes slightly re-arranged.
From me: make the PPP/CHDLC FCS code use "crc32()" to check the 32-bit
FCS.
svn path=/trunk/; revision=8266