Replace sprintf()->snprintf() and strcpy()->strlcpy()

The strcpy() and sprintf() functions are deprecated on some platforms.
Care is needed to ensure correct size is used.  If some platforms
miss snprintf, we can add a #define to sprintf, likewise strlcpy().

The biggest change is adding a size parameter to zfs_id_to_fuidstr().

The various *_impl_get() functions are only used on linux and have
not yet been updated.

Reviewed by: Sean Eric Fagan <sef@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Jorgen Lundman <lundman@lundman.net>
Closes #10400

module/zfs/ddt.c

@@ -253,7 +253,7 @@ void
 ddt_object_name(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
     char *name)
 {
-	(void) sprintf(name, DMU_POOL_DDT,
+	(void) snprintf(name, DDT_NAMELEN, DMU_POOL_DDT,
 	    zio_checksum_table[ddt->ddt_checksum].ci_name,
 	    ddt_ops[type]->ddt_op_name, ddt_class_name[class]);
 }