Replace useCanSockets hack with flexible per-process domain selection

Bug: 158011272
Test: manual
Change-Id: I29d88a42e2309483a740cde9f9a463d83c7a560c
diff --git a/automotive/can/1.0/default/libnetdevice/ifreqs.h b/automotive/can/1.0/default/libnetdevice/ifreqs.h
index 25a40a6..74e5877 100644
--- a/automotive/can/1.0/default/libnetdevice/ifreqs.h
+++ b/automotive/can/1.0/default/libnetdevice/ifreqs.h
@@ -23,6 +23,11 @@
 namespace android::netdevice::ifreqs {
 
 /**
+ * \see useSocketDomain()
+ */
+extern std::atomic_int socketDomain;
+
+/**
  * Sends ioctl interface request.
  *
  * \param request Request type (such as SIOCGIFFLAGS)