Revert "esp: do not unref managed frag pages in esp_ssg_unref()"

This reverts commit 21697720ff43b8dfa25b8e8d9ca7f56f4597fc80.

The patch does not fix the issue completely, so revert for
now and wait for an updated version.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>