netd: Don't fail on FTP or PPTP conntrack failure

The issue has been seen on some Samsung devices.
See https://github.com/phhusson/treble_experimentations/issues/425



Thanks @zamrih for pin-pointing the issue and validating fix

Change-Id: I3d9c865eb5a4b421f9983210c2ceae62b4906234
Signed-off-by: theimpulson <aayushgupta219@gmail.com>