MEDIUM: haterm: Add support for 0-copy data forwading and option to disable it

MEDIUM: haterm: Add support for 0-copy data forwading and option to disable it

The support for the zero-copy data forwarding was added and enabled by
default. The command line option '-dZ' was also added to disable the
feature.

Concretely, when haterm pushes the response payload, if the zero-copy
forwarding is supported, a dedicated function is used to do so.
hstream_ff_snd() will rely on se_nego_ff() to know how many data can send
and at the end, on se_done_ff() to really send data.

hstream_add_ff_data() function was added to perform the raw copy of the
payload in the sedesc I/O buffer.