net-test: fix tearDown bpf reattach logic

Test: TreeHugger
Bug: 285795355
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ib03c04efb4ed183ef49bad9574483816514bfe2b
diff --git a/net/test/bpf_test.py b/net/test/bpf_test.py
index 46ed827..82ff5be 100755
--- a/net/test/bpf_test.py
+++ b/net/test/bpf_test.py
@@ -528,24 +528,27 @@
       os.close(self.map_fd)
       self.map_fd = None
     try:
-      BpfProgDetach(self._cg_fd, BPF_CGROUP_INET_INGRESS)
-      if self.cg_inet_ingress is not None:
+      if self.cg_inet_ingress is None:
+        BpfProgDetach(self._cg_fd, BPF_CGROUP_INET_INGRESS)
+      else:
         BpfProgAttach(self.cg_inet_ingress, self._cg_fd, BPF_CGROUP_INET_INGRESS)
         os.close(self.cg_inet_ingress)
         self.cg_inet_ingress = None
     except socket.error:
       pass
     try:
-      BpfProgDetach(self._cg_fd, BPF_CGROUP_INET_EGRESS)
-      if self.cg_inet_egress is not None:
+      if self.cg_inet_egress is None:
+        BpfProgDetach(self._cg_fd, BPF_CGROUP_INET_EGRESS)
+      else:
         BpfProgAttach(self.cg_inet_egress, self._cg_fd, BPF_CGROUP_INET_EGRESS)
         os.close(self.cg_inet_egress)
         self.cg_inet_egress = None
     except socket.error:
       pass
     try:
-      BpfProgDetach(self._cg_fd, BPF_CGROUP_INET_SOCK_CREATE)
-      if self.cg_inet_sock_create is not None:
+      if self.cg_inet_sock_create is None:
+        BpfProgDetach(self._cg_fd, BPF_CGROUP_INET_SOCK_CREATE)
+      else:
         BpfProgAttach(self.cg_inet_sock_create, self._cg_fd, BPF_CGROUP_INET_SOCK_CREATE)
         os.close(self.cg_inet_sock_create)
         self.cg_inet_sock_create = None