link executor: Add support for interface aliases.

Signed-off-by: Maximilian Wilhelm <max@sdn.clinic>

doc/interfaces.scd

@@ -70,6 +70,9 @@ the system will only respond to certain keywords by default:
 	Denotes the link-type of the interface. When set to _dummy_,
 	the interface is created as a virtual dummy interfaces.
 
+*alias* _alias_
+	Sets the given alias on the interface.
+
 *requires* _interfaces_...
 	Designates one or more required interfaces that must be
 	brought up before configuration of the parent interface.

executor-scripts/linux/link

@@ -70,6 +70,11 @@ up|down)
 	fi
 
 	${MOCK} ip link set $PHASE dev $IFACE $IF_LINK_OPTIONS
+
+	# Set alias is configured
+	if [ "${IF_ALIAS}" ]; then
+		${MOCK} ip link set alias "${IF_ALIAS}" dev "${IFACE}"
+	fi
 	;;
 post-down)
 	if [ "${IF_LINK_TYPE}" = "dummy" ]; then