Add getmtu and setmtu interface commands

Bug: 9372485

Change-Id: I0dfa6b1f973426d67f976a9c79be8de90e3d9c19
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>
diff --git a/NetdConstants.cpp b/NetdConstants.cpp
index 1ab09a5..c3c16eb 100644
--- a/NetdConstants.cpp
+++ b/NetdConstants.cpp
@@ -122,3 +122,24 @@
     close(fd);
     return 0;
 }
+
+int readFile(const char *path, char *buf, int *sizep)
+{
+    int fd = open(path, O_RDONLY);
+    int size;
+
+    if (fd < 0) {
+        ALOGE("Failed to open %s: %s", path, strerror(errno));
+        return -1;
+    }
+
+    size = read(fd, buf, *sizep);
+    if (size < 0) {
+        ALOGE("Failed to write %s: %s", path, strerror(errno));
+        close(fd);
+        return -1;
+    }
+    *sizep = size;
+    close(fd);
+    return 0;
+}