treewide: uapi: Replace zero-length arrays with flexible-array members

There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.
Kernel code should always use “flexible array members”[1] for these
cases. The older style of one-element or zero-length arrays should
no longer be used[2].

This code was transformed with the help of Coccinelle:
(linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file script.cocci --include-headers --dir . > output.patch)

@@
identifier S, member, array;
type T1, T2;
@@

struct S {
  ...
  T1 member;
  T2 array[
- 0
  ];
};

-fstrict-flex-arrays=3 is coming and we need to land these changes
to prevent issues like these in the short future:

../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination buffer has size 0,
but the source string has length 2 (including NUL byte) [-Wfortify-source]
		strcpy(de3->name, ".");
		^

Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If
this breaks anything, we can use a union with a new member name.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/78
Build-tested-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp@intel.com/
Acked-by: Dan Williams <dan.j.williams@intel.com> # For ndctl.h
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

include/uapi/linux/if_arcnet.h

@@ -60,7 +60,7 @@ struct arc_rfc1201 {
 	__u8  proto;		/* protocol ID field - varies		*/
 	__u8  split_flag;	/* for use with split packets		*/
 	__be16   sequence;	/* sequence number			*/
-	__u8  payload[0];	/* space remaining in packet (504 bytes)*/
+	__u8  payload[];	/* space remaining in packet (504 bytes)*/
 };
 #define RFC1201_HDR_SIZE 4
 
@@ -69,7 +69,7 @@ struct arc_rfc1201 {
  */
 struct arc_rfc1051 {
 	__u8 proto;		/* ARC_P_RFC1051_ARP/RFC1051_IP	*/
-	__u8 payload[0];	/* 507 bytes			*/
+	__u8 payload[];	/* 507 bytes			*/
 };
 #define RFC1051_HDR_SIZE 1
 
@@ -80,7 +80,7 @@ struct arc_rfc1051 {
 struct arc_eth_encap {
 	__u8 proto;		/* Always ARC_P_ETHER			*/
 	struct ethhdr eth;	/* standard ethernet header (yuck!)	*/
-	__u8 payload[0];	/* 493 bytes				*/
+	__u8 payload[];	/* 493 bytes				*/
 };
 #define ETH_ENCAP_HDR_SIZE 14