seafile-seahub: fix python-package.mk include

This include is a bit special, because it's the
package that uses OpenWrt's mk rule.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

net/seafile-seahub/patches/020-Makefile-fixes.patch

@@ -3,7 +3,7 @@ diff -rupN seafile-seahub-6.2.2.orig/Makefile seafile-seahub-6.2.2/Makefile
 +++ seafile-seahub-6.2.2/Makefile	2017-10-22 22:46:18.007470936 +0200
 @@ -1,3 +1,6 @@
 +include $(TOPDIR)/rules.mk
-+$(call include_mk, python-package.mk)
++include $(TOPDIR)/feeds/packages/lang/python/python-package.mk
 +
  PROJECT=seahub