net: tcp2: Handle the packet clone error in tcp_data_get()

Unsuccessfull packet clone in tcp_data_get() isn't handled,
add an error handling and don't ACK the incoming data in this case.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Oleg Zhurakivskyy <oleg.zhurakivskyy@intel.com>