Description: ipv6_sockglue: Fix a missing-check bug in ip6_ra_control()
References:
 https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/?id=95baa60a0da80a0143e3ddd4d3725758b4513825
 https://lkml.org/lkml/2019/5/25/229
Notes:
 bwh> There was already a null check before dereferencing the pointer.
 bwh> No security impact.
Bugs:
upstream: N/A "Invalid issue"
4.19-upstream-stable: N/A "Invalid issue"
4.9-upstream-stable: N/A "Invalid issue"
3.16-upstream-stable: N/A "Invalid issue"
sid: N/A "Invalid issue"
4.9-stretch-security: N/A "Invalid issue"
3.16-jessie-security: N/A "Invalid issue"