[FS#312] GRE tunnel fail to up if df option set to 0

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - Alexey (ambientsummer) 

Attached to Project - LEDE Project
Summary - GRE tunnel fail to up if df option set to 0
Task Type - Bug Report
Category - Packages
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - GRE tunnel fail to up if df option set to 0. Everything fine if df option set to 1 or unset.

Device: Xiaomi MiWiFi Mini
LEDE: r2292

config.diff
CONFIG_TARGET_ramips=y
CONFIG_TARGET_ramips_mt7620=y
CONFIG_TARGET_ramips_mt7620_DEVICE_miwifi-mini=y
CONFIG_DROPBEAR_ECC=y
CONFIG_LIBSODIUM_MINIMAL=y
CONFIG_OPENVPN_polarssl_ENABLE_LZO=y
CONFIG_OPENVPN_polarssl_ENABLE_SMALL=y
CONFIG_PACKAGE_dnscrypt-proxy=y
CONFIG_PACKAGE_dnscrypt-proxy-resolvers=y
# CONFIG_PACKAGE_dnsmasq is not set
CONFIG_PACKAGE_dnsmasq-full=y
CONFIG_PACKAGE_dnsmasq_full_dnssec=y
CONFIG_PACKAGE_dnsmasq_full_ipset=y
CONFIG_PACKAGE_dnsmasq_full_noid=y
CONFIG_PACKAGE_gre=y
CONFIG_PACKAGE_grev4=y
CONFIG_PACKAGE_kmod-gre=y
CONFIG_PACKAGE_kmod-ipt-ipset=y
CONFIG_PACKAGE_kmod-iptunnel=y
CONFIG_PACKAGE_kmod-nfnetlink=y
CONFIG_PACKAGE_kmod-tun=y
CONFIG_PACKAGE_libgmp=y
CONFIG_PACKAGE_liblzo=y
CONFIG_PACKAGE_libnettle=y
CONFIG_PACKAGE_libpolarssl=y
CONFIG_PACKAGE_libsodium=y
CONFIG_PACKAGE_openvpn-polarssl=y
CONFIG_PACKAGE_resolveip=y
# CONFIG_OPENVPN_polarssl_ENABLE_DEF_AUTH is not set
# CONFIG_OPENVPN_polarssl_ENABLE_FRAGMENT is not set
# CONFIG_OPENVPN_polarssl_ENABLE_HTTP is not set
# CONFIG_OPENVPN_polarssl_ENABLE_MULTIHOME is not set
# CONFIG_OPENVPN_polarssl_ENABLE_PF is not set
# CONFIG_OPENVPN_polarssl_ENABLE_PORT_SHARE is not set
# CONFIG_OPENVPN_polarssl_ENABLE_SERVER is not set
# CONFIG_OPENVPN_polarssl_ENABLE_SOCKS is not set
# CONFIG_PACKAGE_dnsmasq_full_auth is not set
# CONFIG_PACKAGE_dnsmasq_full_conntrack is not set
# CONFIG_PACKAGE_dnsmasq_full_dhcpv6 is not set
# CONFIG_PACKAGE_kmod-nf-conntrack-netlink is not set
# CONFIG_PACKAGE_libmnl is not set
# CONFIG_PACKAGE_libnetfilter-conntrack is not set
# CONFIG_PACKAGE_libnfnetlink is not set
/etc/config/network
...
config interface 'vpn0'
        option proto 'gre'
        option peeraddr '1.2.3.4'
        option zone 'vpn'
        option mtu '1468'
        option df '0'

config interface 'vpn0_addr'
        option proto 'static'
        option ifname '@vpn0'
        option ipaddr '172.16.4.6'
        option netmask '255.255.255.252'
...
logread
Mon Nov 28 11:07:16 2016 daemon.notice netifd: vpn0 (20451): Command failed: Unknown error
Mon Nov 28 11:07:16 2016 daemon.notice netifd: Interface 'vpn0' is now down
Mon Nov 28 11:07:16 2016 daemon.notice netifd: Interface 'vpn0' is setting up now
Mon Nov 28 11:07:16 2016 daemon.notice netifd: vpn0 (20475): Command failed: Unknown error
Mon Nov 28 11:07:16 2016 daemon.notice netifd: Interface 'vpn0' is now down
Mon Nov 28 11:07:16 2016 daemon.notice netifd: Interface 'vpn0' is setting up now
Mon Nov 28 11:07:16 2016 daemon.notice netifd: vpn0 (20499): Command failed: Unknown error
Mon Nov 28 11:07:16 2016 daemon.notice netifd: Interface 'vpn0' is now down
Mon Nov 28 11:07:16 2016 daemon.notice netifd: Interface 'vpn0' is setting up now
Mon Nov 28 11:07:17 2016 daemon.notice netifd: vpn0 (20524): Command failed: Unknown error
Mon Nov 28 11:07:17 2016 daemon.notice netifd: Interface 'vpn0' is now down
Mon Nov 28 11:07:17 2016 daemon.notice netifd: Interface 'vpn0' is setting up now

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=312