bpf/progs/offload.c: split 4.14/4.19/5.4 into 4.14/4.19 & 5.4

Prep work to allow 5.4+ specific implementation.

Bug: 419747540
Test: TreeHugger
Flag: EXEMPT mainline
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I8aa40b3e2c068e39b34bff3d8c58cc8feccbf139
1 file changed