CONTRIB: debug/flags: add check for SF_ERR_CHK_PORT

This flag was added by commit 95db2bc ("MAJOR: check: find out which
port to use for health check at run time"), let's check for it.
diff --git a/contrib/debug/flags.c b/contrib/debug/flags.c
index dfc813a..bc71bde 100644
--- a/contrib/debug/flags.c
+++ b/contrib/debug/flags.c
@@ -320,6 +320,7 @@
 	case SF_ERR_DOWN:     f &= ~SF_ERR_MASK ; printf("SF_ERR_DOWN%s",     f ? " | " : ""); break;
 	case SF_ERR_KILLED:   f &= ~SF_ERR_MASK ; printf("SF_ERR_KILLED%s",   f ? " | " : ""); break;
 	case SF_ERR_UP:       f &= ~SF_ERR_MASK ; printf("SF_ERR_UP%s",       f ? " | " : ""); break;
+	case SF_ERR_CHK_PORT: f &= ~SF_ERR_MASK ; printf("SF_ERR_CHK_PORT%s",       f ? " | " : ""); break;
 	}
 
 	SHOW_FLAG(f, SF_TUNNEL);