MINOR: spoe: Add max-waiting-frames directive in spoe-agent configuration

This is the maximum number of frames waiting for an acknowledgement on the same
connection. This value is only used when the pipelinied or asynchronus exchanges
between HAProxy and SPOA are enabled. By default, it is set to 20.
diff --git a/src/flt_spoe.c b/src/flt_spoe.c
index 5848fdc..8694b07 100644
--- a/src/flt_spoe.c
+++ b/src/flt_spoe.c
@@ -3455,6 +3455,23 @@
 			goto out;
 		}
 	}
+	else if (!strcmp(args[0], "max-waiting-frames")) {
+		if (!*args[1]) {
+			ha_alert("parsing [%s:%d] : '%s' expects an integer argument.\n",
+				 file, linenum, args[0]);
+                        err_code |= ERR_ALERT | ERR_FATAL;
+                        goto out;
+                }
+		if (alertif_too_many_args(1, file, linenum, args, &err_code))
+			goto out;
+		curagent->max_fpa = atol(args[1]);
+		if (curagent->max_fpa < 1) {
+			ha_alert("parsing [%s:%d] : '%s' expects a positive integer argument.\n",
+				 file, linenum, args[0]);
+			err_code |= ERR_ALERT | ERR_FATAL;
+			goto out;
+		}
+	}
 	else if (!strcmp(args[0], "register-var-names")) {
 		int   cur_arg;