Description: ip_sockglue: Fix missing-check bug in ip_ra_control()
References:
 https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/?id=425aa0e1d01513437668fa3d4a971168bbaa8515
 https://lkml.org/lkml/2019/5/25/230 
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"