Improve BPF tethering counters.

Test: m
Change-Id: I53961e1e16bf90d76f16b9416c55b65e8374373d
diff --git a/Tethering/bpf_progs/bpf_tethering.h b/Tethering/bpf_progs/bpf_tethering.h
index 00b16a3..d83ae34 100644
--- a/Tethering/bpf_progs/bpf_tethering.h
+++ b/Tethering/bpf_progs/bpf_tethering.h
@@ -34,6 +34,7 @@
     ERR(BELOW_IPV6_MTU)      \
     ERR(LIMIT_REACHED)       \
     ERR(CHANGE_HEAD_FAILED)  \
+    ERR(TOO_SHORT)           \
     ERR(_MAX)
 
 #define ERR(x) BPF_TETHER_ERR_ ##x,