cxgbe(4): Allow a T6 adapter to switch between TOE and NIC TLS mode.

cxgbe(4): Allow a T6 adapter to switch between TOE and NIC TLS mode.

The hw.cxgbe.kern_tls tunable was used for this in the past and if it
was set then all T6 adapters would be configured for NIC TLS operation
and could not be reconfigured for TOE without a reload.  With this
change ifconfig can be used to manipulate toe and txtls caps like any
other caps.  hw.cxgbe.kern_tls continues to work as usual but its
effects are not permanent any more.

* Enable nic_ktls_ofld in the default configuration file and use the
  firmware instead of direct register manipulation to apply/rollback
  NIC TLS configuration.  This allows the driver to switch the hardware
  between TOE and NIC TLS mode in a safe manner.  Note that the
  configuration is adapter-wide and not per-port.

* Remove the kern_tls config file as it works with 100G T6 cards only
  and leads to firmware crashes with 25G cards.  The configurations
  included with the driver (with the exception of the FPGA configs) are
  supposed to work with all adapters.

Reported by:	Veeresh U.K. at Chelsio
MFC after:	2 weeks
Sponsored by:	Chelsio Communications
Reviewed by:	jhb@
Differential Revision: https://reviews.freebsd.org/D29291