liblog: replace "frontend" with "transport"

We still do not have any users of the 'frontend' interface, let's
right a wrong and rename it to 'transport' as it makes more sense.
Renames android_log_set_frontend, android_log_get_frontend and
include/log/log_frontend.h.

SideEffects: None
Test: gTest liblog-unit-tests
Bug: 27405083
Change-Id: I7c1c0f3dfdc7cf047285403e306edbd16ad1324d
diff --git a/liblog/config_write.c b/liblog/config_write.c
index 2257070..0a8b52f 100644
--- a/liblog/config_write.c
+++ b/liblog/config_write.c
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include <log/log_frontend.h>
+#include <log/log_transport.h>
 
 #include "config_write.h"
 #include "logger.h"
@@ -55,15 +55,15 @@
 }
 
 LIBLOG_HIDDEN void __android_log_config_write() {
-  if (__android_log_frontend & LOGGER_LOCAL) {
+  if (__android_log_transport & LOGGER_LOCAL) {
     extern struct android_log_transport_write localLoggerWrite;
 
     __android_log_add_transport(&__android_log_transport_write,
                                 &localLoggerWrite);
   }
 
-  if ((__android_log_frontend == LOGGER_DEFAULT) ||
-      (__android_log_frontend & LOGGER_LOGD)) {
+  if ((__android_log_transport == LOGGER_DEFAULT) ||
+      (__android_log_transport & LOGGER_LOGD)) {
 #if (FAKE_LOG_DEVICE == 0)
     extern struct android_log_transport_write logdLoggerWrite;
     extern struct android_log_transport_write pmsgLoggerWrite;
@@ -79,7 +79,7 @@
 #endif
   }
 
-  if (__android_log_frontend & LOGGER_STDERR) {
+  if (__android_log_transport & LOGGER_STDERR) {
     extern struct android_log_transport_write stderrLoggerWrite;
 
     /*