Fix issue with zero-length arrays at end of struct

A common practice in C coding, over the years, has been to
add a zero-length array at the end of the structure when trying
to represent a possibly-empty array of bytes that may be
appended to the struct. But the gcc-10 compiler does not
like such structures, taking the zero-length literally.

The following errors are fixed by this commit:

> iscsiadm.c: In function ‘session_stats’:
> iscsiadm.c:939:56: error: array subscript ‘(<unknown>) + -1’ is outside the bounds of an interior zero-length array ‘struct iscsi_stats_custom[0]’ [-Werror=zero-length-bounds]
>   939 |         (unsigned long long)rsp.u.getstats.stats.custom[i].value);
>       |                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
> In file included from initiator.h:29,
>                  from iscsiadm.c:36:
> ../include/iscsi_if.h:844:28: note: while referencing ‘custom’
>   844 |  struct iscsi_stats_custom custom[0]
>       |                            ^~~~~~
> iscsiadm.c:938:56: error: array subscript ‘(<unknown>) + -1’ is outside the bounds of an interior zero-length array ‘struct iscsi_stats_custom[0]’ [-Werror=zero-length-bounds]
>   938 |   printf("\t%s: %llu\n", rsp.u.getstats.stats.custom[i].desc,
>       |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
> In file included from initiator.h:29,
>                  from iscsiadm.c:36:
> ../include/iscsi_if.h:844:28: note: while referencing ‘custom’
>   844 |  struct iscsi_stats_custom custom[0]
>       |                            ^~~~~~
> cc1: all warnings being treated as errors

The work around is to convert the two "custom[0]" structure members to
use "custom[]".

1 files changed, 2 insertions, 2 deletions

diff --git a/include/iscsi_if.h b/include/iscsi_if.h
index 2d46214..5a1c614 100644
--- a/include/iscsi_if.h
+++ b/include/iscsi_if.h
@@ -841,7 +841,7 @@ struct iscsi_stats {
 	 * up to ISCSI_STATS_CUSTOM_MAX
 	 */
 	uint32_t custom_length;
-	struct iscsi_stats_custom custom[0]
+	struct iscsi_stats_custom custom[]
 		__attribute__ ((aligned (sizeof(uint64_t))));
 };
 
@@ -972,7 +972,7 @@ struct iscsi_offload_host_stats {
 	 * up to ISCSI_HOST_STATS_CUSTOM_MAX
 	 */
 	uint32_t custom_length;
-	struct iscsi_host_stats_custom custom[0]
+	struct iscsi_host_stats_custom custom[]
 		 __attribute__ ((aligned (sizeof(uint64_t))));
 };