[fix] add default user-agent data in HTTP Post method

Author: Noyel Seth

esp8266.py

@@ -459,7 +459,7 @@ def doHttpGet(self,host,path,user_agent="RPi-Pico", port=80):
             return 0, None
 
 
-    def doHttpPost(self,host,path,user_agent,content_type,content,port=80):
+    def doHttpPost(self,host,path,user_agent="RPi-Pico",content_type,content,port=80):
         """
         This fucntion use to complete a HTTP Post operation