RHEL7: Very high %sys CPU usage in __neigh_create()

Issue

• We are in the process of migrating our environment from RHEL 6.7 to RHEL 7.5 and we are seeing quite a big difference in %sys kernel CPU usage between these two major versions. The same software is producing less kernel CPU load in RHEL 6.7 than it does in 7.5.
• UDP sendto() occasionally returns -EINVAL. See also: https://access.redhat.com/solutions/2985371, although in this case much larger gc_thresh values are required.