nfp: tls: rename tls packet counters

Align to the naming convention in TLS documentation.

Fixes: 51a5e563 ("nfp: tls: add basic statistics")
Suggested-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>