cxgbe tom: Send auxiliary TLS work requests as raw WR mbufs

In particular, the work request to update the TCB state when switching
from plain TCP to TLS is now queued on the connection's offload
transmit queue rather than over the per-port control queue.

This also handles an unlikely edge case that a connection does not
have sufficient credits to transmit other work requests synchronously
such as programming the key in on-card memory or altering TCB fields.

Reviewed by: np
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D47763

(cherry picked from commit d869395ac4bd248da7c5bdc67afb19ca89fbeeee)