Fix the PPTP Client Connection Issue Under ufw#

Fix the issue of the PPTP client unable to connect in Ubuntu when ufw is enabled.

Edit /etc/ufw/before.rules
Add the following line before COMMIT:
-A ufw-before-input -p 47 -j ACCEPT

Edit /etc/default/ufw
Add nf_conntrack_pptp to the IPT_MODULES option.

Restart ufw
sudo service ufw restart

Reconnect with pptpsetup after the modification.