Add missing description of counters.
Split tx_tls_encrypted counter into two, to give packets
and bytes indications.

Fixes: f42c104f ("Documentation: add TLS offload documentation")
Suggested-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NTariq Toukan <tariqt@mellanox.com>
Signed-off-by: NSaeed Mahameed <saeedm@mellanox.com>