git-p4: python3: fix octal constants

See PEP3127. Works fine with python2 as well.

Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -1841,7 +1841,7 @@ class P4Submit(Command, P4UserMap):
                     filesToDelete.remove(path)
 
                 dst_mode = int(diff['dst_mode'], 8)
-                if dst_mode == 0120000:
+                if dst_mode == 0o120000:
                     symlinks.add(path)
 
             elif modifier == "D":