adb: split up reads longer than 16k.

Reads from functionfs allocate contiguous buffers in the kernel, causing
long ones to sometimes fail because of memory fragmentation.

Bug: http://b/26206622
Change-Id: Id40753d6f29b37b5ca97c3e2fa3921f52b4242de

adb/usb_linux_client.cpp

@@ -481,7 +481,8 @@ static int usb_ffs_read(usb_handle* h, void* data, int len) {
 
     char* buf = static_cast<char*>(data);
     while (len > 0) {
-        int n = adb_read(h->bulk_out, buf, len);
+        int read_len = (len > 16384) ? 16384 : len;
+        int n = adb_read(h->bulk_out, buf, read_len);
         if (n < 0) {
             D("ERROR: fd = %d, n = %d: %s", h->bulk_out, n, strerror(errno));
             return -1;