Use the (un)marshalling functions scsi_get/set_uint16/32() anywhere in the code

This has the nice side effect to remove the compiler warning
"dereferencing type-punned pointer will break strict-aliasing rules"
which occur since gcc-4.7.

There are 79 locations where the warning occurs. All of them are in
statements where the htonl/htons/ntohl/ntohs functions are used, e.g.:

in lib/pdu.c                itt = ntohl(*(uint32_t *)&in->hdr[16]);
in lib/scsi-lowlevel.c      *(uint32_t *)&task->cdb[2] = htonl(lba);

The warning is not related to the htonl/htons/ntohl/ntohs functions but
to the casting/dereferencing operation. If the dereferenced variable is
already a pointer, the warning does not not occur, e.g. this one:

in lib/pdu.c                itt = ntohl(*(uint32_t *)&in->data[16]);

The warning is caused by the -fstrict-aliasing option. The
-fstrict-aliasing option is enabled at optimization levels -O2, -O3, -Os.

Signed-off-by: Bernhard Kohl <bernhard.kohl@gmx.net>

lib/task_mgmt.c

@@ -87,7 +87,7 @@ iscsi_process_task_mgmt_reply(struct iscsi_context *iscsi, struct iscsi_pdu *pdu
 
 	response = in->hdr[2];
 
-	maxcmdsn = ntohl(*(uint32_t *)&in->hdr[32]);
+	maxcmdsn = scsi_get_uint32(&in->hdr[32]);
 	if (maxcmdsn > iscsi->maxcmdsn) {
 		iscsi->maxcmdsn = maxcmdsn;
 	}