use a second map for SingleWriterBpfMap test

because the shared r/w lock on the first
conflicts with the exclusive r/w lock on the second

This fixes roughly *half* the BpfMapTest tests.

Test: TreeHugger, atest BpfMapTest less broken
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I9d500597cad16bb7756df3e6feb9a7aa762e59d9
diff --git a/tests/mts/bpf_existence_test.cpp b/tests/mts/bpf_existence_test.cpp
index dca9dd7..1dc2e90 100644
--- a/tests/mts/bpf_existence_test.cpp
+++ b/tests/mts/bpf_existence_test.cpp
@@ -68,6 +68,7 @@
     TETHERING "map_offload_tether_upstream6_map",
     TETHERING "map_test_bitmap",
     TETHERING "map_test_tether_downstream6_map",
+    TETHERING "map_test_tether2_downstream6_map",
     TETHERING "prog_offload_schedcls_tether_downstream4_ether",
     TETHERING "prog_offload_schedcls_tether_downstream4_rawip",
     TETHERING "prog_offload_schedcls_tether_downstream6_ether",