net-test: not supported in netns before 4.15 if BH_TIMEOUT_SYSCTL does not exist. Related to the following CL which is included in 4.15: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3733be14a32bae288b61ed28341e593baba983af Change-Id: I1cc9b9c79a1eec83c47d36790c8f944b0261ff32 Merged-In: I1cc9b9c79a1eec83c47d36790c8f944b0261ff32 Test: Run vts_kernel_net_tests with Ethernet or Wi-Fi connected Bug: 204306357 (cherry picked from commit 7b07e88d38aa3211f47dc1fcd360399d75514479)