use new sdbus++ camelcase

Change I17a8d7479556596a3cf252b3f4eae9c8df547189 will change
how sdbus++ generates names which start with an acronym.
Prepare for this by keying off the SDBUSPP_NEW_CAMELCASE
define to use the new format.

Changes:
    vLAN -> vlan

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I3c5c1d0d14c7f7b0e99da57477aa117c39114021
diff --git a/network_manager.cpp b/network_manager.cpp
index 10a2573..881b767 100644
--- a/network_manager.cpp
+++ b/network_manager.cpp
@@ -180,7 +180,7 @@
         bus, objPath.string(), *this);
 }
 
-ObjectPath Manager::vLAN(IntfName interfaceName, uint32_t id)
+ObjectPath Manager::vlan(IntfName interfaceName, uint32_t id)
 {
     return interfaces[interfaceName]->createVLAN(id);
 }