socket: Add constants for basic multicast support.

socket/socket.py

@@ -3,6 +3,10 @@ import usocket as _socket
 
 
 _GLOBAL_DEFAULT_TIMEOUT = 30
+IPPROTO_IP = 0
+IP_ADD_MEMBERSHIP = 35
+IP_DROP_MEMBERSHIP = 36
+
 
 def create_connection(addr, timeout=None, source_address=None):
     s = socket()