Documentation: TLS: fix stat counters description

Following minimum set of TLS-related statistics should be reported

by the driver:

 * ``rx_tls_decrypted`` - number of successfully decrypted TLS segments

 * ``tx_tls_encrypted`` - number of in-order TLS segments passed to device

   for encryption

 * ``rx_tls_decrypted_packets`` - number of successfully decrypted RX packets

   which were part of a TLS stream.

 * ``rx_tls_decrypted_bytes`` - number of TLS payload bytes in RX packets

   which were successfully decrypted.

 * ``tx_tls_encrypted_packets`` - number of TX packets passed to the device

   for encryption of their TLS payload.

 * ``tx_tls_encrypted_bytes`` - number of TLS payload bytes in TX packets

   passed to the device for encryption.

 * ``tx_tls_ctx`` - number of TLS TX HW offload contexts added to device for

   encryption.

 * ``tx_tls_ooo`` - number of TX packets which were part of a TLS stream

   but did not arrive in the expected order

 * ``tx_tls_drop_no_sync_data`` - number of TX packets dropped because

   they arrived out of order and associated record could not be found

   but did not arrive in the expected order.

 * ``tx_tls_drop_no_sync_data`` - number of TX packets which were part of

   a TLS stream dropped, because they arrived out of order and associated

   record could not be found.

 * ``tx_tls_drop_bypass_req`` - number of TX packets which were part of a TLS

   stream dropped, because they contain both data that has been encrypted by

   software and data that expects hardware crypto offload.

Notable corner cases, exceptions and additional requirements

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