net/tls: Constify base proto ops used for building tls proto

The helper that builds kTLS proto ops doesn't need to and should not modify
the base proto ops. Annotate the parameter as read-only.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>