[FS#1083] ar71xx Kernel 4.9 PPTP Passthrough not working

[LEDE Bugs]

The following task has a new comment added:

FS#1083 - ar71xx Kernel 4.9  PPTP Passthrough not working
User who did this - Martin Bouska (maabo)

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And I confirm, that after building image from trunk source with KERNEL_PATCHVER:=4.4 the problem disappeared.
**pptp works fine with older kernel**
All other options in .config remains same as it was before with 4.9 kernel.

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https://bugs.lede-project.org/index.php?do=details&task_id=1083#comment3934