Description: udp: fix GRO packet of death
References:
 https://www.spinics.net/lists/netdev/msg568315.html
Notes:
 carnil> Fixes: e20cf8d3f1f7 ("udp: implement GRO for plain UDP
 carnil> sockets.") which is introduced in 5.0-rc1
Bugs:
upstream: released (5.1) [4dd2b82d5adfbe0b1587ccad7a8f76d826120f37]
4.19-upstream-stable: N/A "Vulnerable code introduced later in 5.0-rc1"
4.9-upstream-stable: N/A "Vulnerable code introduced later in 5.0-rc1" 
3.16-upstream-stable: N/A "Vulnerable code introduced later in 5.0-rc1"
sid: N/A "Vulnerable code introduced later"
4.9-stretch-security: N/A "Vulnerable code introduced later"
3.16-jessie-security: N/A "Vulnerable code introduced later"