net/netfilter: fix visual studio Compiler Error C2229

D:\archer\code\nuttx\include\nuttx/net/netfilter/x_tables.h(71,7):
  error C2229: type 'struct xt_standard_target' has an illegal zero-sized array

Compiler error C2229:
A member of a structure or bit field contains a zero-sized array that is not the last member.

Reference:
https://learn.microsoft.com/en-us/cpp/error-messages/compiler-errors-1/compiler-error-c2229?view=msvc-170

Signed-off-by: chao an <anchao@xiaomi.com>

Author: anchao

include/nuttx/net/netfilter/ip_tables.h

@@ -117,7 +117,7 @@ struct ipt_entry
 
   struct xt_counters counters; /* Packet and byte counters. */
 
-  unsigned char elems[0];      /* The matches (if any), then the target. */
+  unsigned char elems[1];      /* The matches (if any), then the target. */
 };
 
 /* Note 1: How entries are organized in following interface arguments.

include/nuttx/net/netfilter/x_tables.h

@@ -62,7 +62,7 @@ struct xt_entry_target
       uint16_t target_size; /* Total length */
     } u;
 
-  unsigned char data[0];
+  unsigned char data[1];
 };
 
 struct xt_standard_target