systemd-networkd: configure based on type rather than name, add a comment on MACAddress matching

Resolves: warnings on potentially unpredictable interface names.

etc/systemd/network/ethernet.network

@@ -1,5 +1,8 @@
 [Match]
-Name=eth0
+#Name=*
+# Can be {colon,hyphen,dot}-delimited hexadecimal or IPv{4,6} address
+#MACAddress=
+Type=ether
 
 [Link]
 # My devices generally also have WiFi so lack of ethernet is not a reason

etc/systemd/network/wlan.network

@@ -1,5 +1,8 @@
 [Match]
-Name=wlan0
+#Name=*
+# Can be {colon,hyphen,dot}-delimited hexadecimal or IPv{4,6} address
+#MACAddress=
+Type=wlan
 
 [Link]
 # Always set administrative state to up. Implies RequiredForOnline=yes