Update link in the pos for offline and online mode from pos settings (#11061)

erpnext/accounts/doctype/pos_settings/pos_settings.py

@@ -3,7 +3,17 @@
 # For license information, please see license.txt
 
 from __future__ import unicode_literals
+import frappe
 from frappe.model.document import Document
 
 class POSSettings(Document):
-	pass
+	def validate(self):
+		self.set_link_for_pos()
+
+	def set_link_for_pos(self):
+		link = 'pos' if self.use_pos_in_offline_mode else 'point-of-sale'
+		desktop_icon = frappe.db.get_value('Desktop Icon',
+			{'standard': 1, 'module_name': 'POS'}, 'name')
+
+		if desktop_icon:
+			frappe.db.set_value('Desktop Icon', desktop_icon, 'link', link)