tls: remove tls_context argument from tls_set_sw_offload

It's not really needed since we end up refetching it as tls_ctx. We
can also remove the NULL check, since we have already dereferenced ctx
in do_tls_setsockopt_conf.

Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>