qcacmn: Include enet.h for ETHERTYPE_VLAN_LEN macro definition

ETHERTYPE_VLAN_LEN is defined in enet.h, which is not being
included in dp_main.c, which can lead to compilation error
if the MULTIPASS feature is enabled.

Include the enet.h header file for ETHERTYPE_VLAN_LEN macro
definition

Change-Id: I589123a0e2161486a430c6e8d6ca18e5907252d4
CRs-Fixed: 3494435

dp/wifi3.0/dp_main.c

@@ -55,6 +55,9 @@
 #include "qdf_mem.h"   /* qdf_mem_malloc,free */
 #include "cfg_ucfg_api.h"
 #include <wlan_module_ids.h>
+#ifdef QCA_MULTIPASS_SUPPORT
+#include <enet.h>
+#endif
 
 #ifdef QCA_LL_TX_FLOW_CONTROL_V2
 #include "cdp_txrx_flow_ctrl_v2.h"