Un-drop support for pre-4.14 kernels.

This effectively reverts commit 6ed2ab9b,
while ensuring that the program has the right permissions as
defined in r.android.com/2130014 :

oriole:/ # ls -lZ /sys/fs/bpf/netd_shared/prog_netd_cgroupsock_inet_create
-r--r----- 1 root root u:object_r:fs_bpf_netd_readonly:s0  0 2022-10-27 20:05 /sys/fs/bpf/netd_shared/prog_netd_cgroupsock_inet_create

Reason for revert: need to support 4.9 devices upgrading to T.

The only thing that cannot currently be supported on those
devices is the inet_create program which implements the
INTERNET permission.

Also, update bpf_existence_test so it does not check for the
existence of the program on pre-4.14 devices.

Bug: 254001921
Test: atest bpf_existence_test
Change-Id: I14f26cee5feeaae93b4d9710a7b9a2f835ff405f