rename variable serial_device to serial_ir_device

and add an entry for the serial-ir role to the playbook (commented out
by default, so the user has to enable it if required)

roles/serial-ir/defaults/main.yml

@@ -1,2 +1,2 @@
 ---
-serial_device: ttyS0
+serial_ir_device: ttyS0

roles/serial-ir/templates/modprobe.d/serial_ir.conf.j2

@@ -1,8 +1,8 @@
 #COM1 equivalent, /dev/ttyS0
-{% if serial_device == "ttyS0" %}
+{% if serial_ir_device == "ttyS0" %}
 options serial_ir irq=4 io=0x3f8
-{% elif serial_device == "ttyS1" %}
+{% elif serial_ir_device == "ttyS1" %}
 #COM2 equivalent, /dev/ttyS1
 options serial_ir irq=3 io=0x2f8
 {% endif %}
-install serial_ir setserial /dev/{{serial_device}} uart none; /sbin/modprobe --ignore-install serial_ir
+install serial_ir setserial /dev/{{serial_ir_device}} uart none; /sbin/modprobe --ignore-install serial_ir

roles/serial-ir/templates/serial.conf.j2

@@ -1,7 +1,7 @@
-{% if serial_device == "ttyS0" %}
+{% if serial_ir_device == "ttyS0" %}
 #COM1 equivalent, /dev/ttyS0
 /dev/ttyS0 uart none
-{% elif serial_device == "ttyS1" %}
+{% elif serial_ir_device == "ttyS1" %}
 #COM2 equivalent, /dev/ttyS1
 /dev/ttyS1 uart none
 {% endif %}