net: ovs: fix ovs_drop_reasons error

There is something wrong with ovs_drop_reasons. ovs_drop_reasons[0] is
"OVS_DROP_LAST_ACTION", but OVS_DROP_LAST_ACTION == __OVS_DROP_REASON + 1,
which means that ovs_drop_reasons[1] should be "OVS_DROP_LAST_ACTION".

And as Adrian tested, without the patch, adding flow to drop packets
results in:

drop at: do_execute_actions+0x197/0xb20 [openvsw (0xffffffffc0db6f97)
origin: software
input port ifindex: 8
timestamp: Tue Aug 20 10:19:17 2024 859853461 nsec
protocol: 0x800
length: 98
original length: 98
drop reason: OVS_DROP_ACTION_ERROR

With the patch, the same results in:

drop at: do_execute_actions+0x197/0xb20 [openvsw (0xffffffffc0db6f97)
origin: software
input port ifindex: 8
timestamp: Tue Aug 20 10:16:13 2024 475856608 nsec
protocol: 0x800
length: 98
original length: 98
drop reason: OVS_DROP_LAST_ACTION

Fix this by initializing ovs_drop_reasons with index.

Fixes: 9d802da4 ("net: openvswitch: add last-action drop reason")
Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Tested-by: Adrian Moreno <amorenoz@redhat.com>
Reviewed-by: Adrian Moreno <amorenoz@redhat.com>
Link: https://patch.msgid.link/20240821123252.186305-1-dongml2@chinatelecom.cnSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/openvswitch/datapath.c

@@ -2706,7 +2706,7 @@ static struct pernet_operations ovs_net_ops = {
 };
 
 static const char * const ovs_drop_reasons[] = {
-#define S(x)	(#x),
+#define S(x) [(x) & ~SKB_DROP_REASON_SUBSYS_MASK] = (#x),
 	OVS_DROP_REASONS(S)
 #undef S
 };