platform: reuse nm_ip_addr_zero for a all-zero ethernet MAC address

src/platform/nm-platform.h

@@ -96,6 +96,11 @@ typedef struct {
 		guint8 addr_ptr[1];
 		in_addr_t addr4;
 		struct in6_addr addr6;
+
+		/* NMIPAddr is really a union for IP addresses.
+		 * However, as ethernet addresses fit in here nicely, ruse
+		 * it also for an ethernet MAC address. */
+		guint8 addr_eth[6 /*ETH_ALEN*/];
 	};
 } NMIPAddr;