xerox_mfp: Add Samsung Xpress C1860FW

Device status is “untested”, because it was not really tested _in depth_.
Basic scanning of a number of pages using the automated feeder worked.

See https://alioth-lists.debian.net/pipermail/sane-devel/2018-October/036411.html

backend/xerox_mfp.conf.in

@@ -196,6 +196,9 @@ usb 0x04e8 0x3466
 #Samsung C460 Series
 usb 0x04e8 0x3468
 
+#Samsung C1860FW
+usb 0x04e8 0x346b
+
 #Samsung M458x Series
 usb 0x04e8 0x346f
 

doc/descriptions/xerox_mfp.desc

@@ -383,6 +383,11 @@
 :usbid "0x04e8" "0x3468"
 :status :untested
 
+:model "C1860FW"
+:interface "USB"
+:usbid "0x04e8" "0x346b"
+:status :untested
+
 :model "M458x Series"
 :interface "USB"
 :usbid "0x04e8" "0x346f"