net/tls: add statistics for installed sessions

Add SNMP stats for number of sockets with successfully
installed sessions.  Break them down to software and
hardware ones.  Note that if hardware offload fails
stack uses software implementation, and counts the
session appropriately.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/tls.rst

@@ -219,3 +219,17 @@ Statistics
 
 TLS implementation exposes the following per-namespace statistics
 (``/proc/net/tls_stat``):
+
+- ``TlsCurrTxSw``, ``TlsCurrRxSw`` -
+  number of TX and RX sessions currently installed where host handles
+  cryptography
+
+- ``TlsCurrTxDevice``, ``TlsCurrRxDevice`` -
+  number of TX and RX sessions currently installed where NIC handles
+  cryptography
+
+- ``TlsTxSw``, ``TlsRxSw`` -
+  number of TX and RX sessions opened with host cryptography
+
+- ``TlsTxDevice``, ``TlsRxDevice`` -
+  number of TX and RX sessions opened with NIC cryptography