MINOR: backend: rework the LC definition to support other connection-based algos

The leastconn algorithm should be of kind "connection-based", not "leastconn"
if we want to later support other connection-based LB algos.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 77f0c5d..b157934 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -6205,7 +6205,7 @@
 			}
 			break;
 
-		case BE_LB_KIND_LC:
+		case BE_LB_KIND_CB:
 			curproxy->lbprm.algo |= BE_LB_LKUP_LCTREE | BE_LB_PROP_DYN;
 			fwlc_init_server_tree(curproxy);
 			break;