Description: race condition in l2tp tunnel handling
References:
 https://source.android.com/security/bulletin/pixel/2018-09-01
Notes:
 carnil> Introduced an ABI change AFAICS so might just be postponed
 carnil> to an update where anyway an ABI bump would be required.
 bwh> l2tp was missing a *lot* of fixes in 4.9, until 4.9.225.
Bugs:
upstream: released (4.14-rc1) [f026bc29a8e093edfbb2a77700454b285c97e8ad]
4.19-upstream-stable: N/A "Fixed before branch point"
4.9-upstream-stable: released (4.9.225) [feaed88dccc4742805c41260040103fa8a7f0df2]
3.16-upstream-stable: released (3.16.51) [0b3ca265e81f5e1d9f7f66ad416cbabecca914cf]
sid: released (4.14.2-1)
4.19-buster-security: N/A "Fixed before branching point"
4.9-stretch-security: released (4.9.228-1)
3.16-jessie-security: released (3.16.51-1)