zstream: consolidate shared code

zstream currently contains three identical copies of dump_record(),
which appear to all be drawn from libzfs_sendrecv.c. The original
is marked internal.

This PR adds zstream_util.[hc] and puts the shared code there along with
a couple of other items in common.

No functional changes.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Garth Snyder <garth@garthsnyder.com>
Closes #18284

cmd/zstream/zstream_dump.c

@@ -44,6 +44,7 @@
 #include <sys/zio.h>
 #include <zfs_fletcher.h>
 #include "zstream.h"
+#include "zstream_util.h"
 
 /*
  * If dump mode is enabled, the number of bytes to print per line
@@ -60,18 +61,6 @@ static FILE *send_stream = 0;
 static boolean_t do_byteswap = B_FALSE;
 static boolean_t do_cksum = B_TRUE;
 
-void *
-safe_malloc(size_t size)
-{
-	void *rv = malloc(size);
-	if (rv == NULL) {
-		(void) fprintf(stderr, "ERROR; failed to allocate %zu bytes\n",
-		    size);
-		abort();
-	}
-	return (rv);
-}
-
 /*
  * ssread - send stream read.
  *