[SCSI] zfcp: Fix hexdump data in s390dbf traces

Fix multiple problems found in the hexdump data:
 - length calculation was wrong, traces were incomplete
 - FC payloads were dumped in different record than the output
   function tried to read
 - minor fixes in output
 - allow complete RSCN traces (up to 1024 bytes according to spec)

Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>