BUG/MINOR: http_ana: make sure redirect flags don't have overlapping bits

commit c87e46881 ("MINOR: http-rules: Add a flag on redirect rules to know the
rule direction") introduced a new flag for redirect rules, but its value has
bits in common with REDIRECT_FLAG_DROP_QS, which makes us enter this code path
in http_apply_redirect_rule(), which will then drop the query string.
To fix this, just give REDIRECT_FLAG_FROM_REQ its own unique value.

This must be backported where c87e46881687b8ddb9b3f459e60edb1e8d7c5d7c is backported.

This should fix issue 521.
diff --git a/include/types/http_ana.h b/include/types/http_ana.h
index bc66098..6740c03 100644
--- a/include/types/http_ana.h
+++ b/include/types/http_ana.h
@@ -99,7 +99,7 @@
 	REDIRECT_FLAG_NONE = 0,
 	REDIRECT_FLAG_DROP_QS = 1,	/* drop query string */
 	REDIRECT_FLAG_APPEND_SLASH = 2,	/* append a slash if missing at the end */
-	REDIRECT_FLAG_FROM_REQ = 3,     /* redirect rule on the request path */
+	REDIRECT_FLAG_FROM_REQ = 4,     /* redirect rule on the request path */
 };
 
 /* Redirect types (location, prefix, extended ) */