There is no guarantee that rmnet rx_handler is only fed with linear
skbs, but current rmnet implementation does not check that, leading
to crash in case of non linear skbs processed as linear ones.

Fix that by ensuring skb linearization before processing.
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Acked-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Link: https://lore.kernel.org/r/1612428002-12333-2-git-send-email-loic.poulain@linaro.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>