ebpf offload - do L4 header present check earlier

and more importantly unconditionally.  This requires less effort
on the part of the in-kernel bpf verifier.

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ibaa94bf096fc81c4d984dfabf515131b1c81ef09
diff --git a/Tethering/bpf_progs/bpf_tethering.h b/Tethering/bpf_progs/bpf_tethering.h
index 10e6bb0..4e006db 100644
--- a/Tethering/bpf_progs/bpf_tethering.h
+++ b/Tethering/bpf_progs/bpf_tethering.h
@@ -41,6 +41,7 @@
     ERR(CHECKSUM)            \
     ERR(NON_TCP_UDP)         \
     ERR(NON_TCP)             \
+    ERR(SHORT_L4_HEADER)     \
     ERR(SHORT_TCP_HEADER)    \
     ERR(SHORT_UDP_HEADER)    \
     ERR(TRUNCATED_IPV4)      \