BUG/MINOR: sample: fix backend direction flags consecutive to last fix

Commit 7a06ffb85 ("BUG/MEDIUM: sample: Cumulate frontend and backend
sample validity flags") introduced a typo confusing the request and
the response direction when checking for validity of a rule applied
to a backend. This was reported by Coverity in issue #1417.

This needs to be backported where the patch above is backported.

(cherry picked from commit b39e47a52b19e7b62727393f9b8e8bd36330b550)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/http_htx.c b/src/http_htx.c
index 37ef28a..f0e0a43 100644
--- a/src/http_htx.c
+++ b/src/http_htx.c
@@ -1404,7 +1404,7 @@
 		if (px->cap & PR_CAP_FE)
 			cap |= ((px->conf.args.ctx == ARGC_HRQ) ? SMP_VAL_FE_HRQ_HDR : SMP_VAL_FE_HRS_HDR);
 		if (px->cap & PR_CAP_BE)
-			cap |= ((px->conf.args.ctx == ARGC_HRQ) ? SMP_VAL_BE_HRS_HDR : SMP_VAL_BE_HRS_HDR);
+			cap |= ((px->conf.args.ctx == ARGC_HRQ) ? SMP_VAL_BE_HRQ_HDR : SMP_VAL_BE_HRS_HDR);
 	}
 
 	cur_arg = *orig_arg;