Record hal_tetheroffload_service for compatibility.

Commit: e58a8de5 added a new type
which has no analogue in 26.0.  Record it as such.

Bug: 62573845
Test: None. Prebuilt change only.
Change-Id: I6b6d2aa64e0ac2c39c8d0427d333e6c7fc2b0bb1

prebuilts/api/26.0/26.0.ignore.cil

@@ -7,6 +7,7 @@
     e2fs
     e2fs_exec
     hal_cas_hwservice
+    hal_tetheroffload_hwservice
     kmsg_debug_device
     memcg_device
     netd_stable_secret_prop