MINOR: samples: extract the anonymous union and create the union sample_value

This extract is not really required, but it maybe will be usefull later.
A comming soonpatch about simplification of stick table values will
use this union

include/types/sample.h

@@ -242,16 +242,18 @@ struct meth {
 	struct chunk str;
 };
 
-/* Used to store sample constant */
-struct sample_data {
-	int type;                 /* SMP_T_* */
-	union {
+union sample_value {
 	long long int   sint;  /* used for signed 64bits integers */
 	struct in_addr  ipv4;  /* used for ipv4 addresses */
 	struct in6_addr ipv6;  /* used for ipv6 addresses */
 	struct chunk    str;   /* used for char strings or buffers */
 	struct meth     meth;  /* used for http method */
-	} data;                        /* sample data */
+};
+
+/* Used to store sample constant */
+struct sample_data {
+	int type;                 /* SMP_T_* */
+	union sample_value data;  /* sample data */
 };
 
 /* a sample is a typed data extracted from a stream. It has a type, contents,