wext: uninline stream addition functions

With 78, 111 and 85 bytes respectively (on x86-64), the
functions iwe_stream_add_event(), iwe_stream_add_point()
and iwe_stream_add_value() really shouldn't be inlines.

It appears that at least my compiler already decided
the same, and created a single instance of each one
of them for each file using it, but that's still a
number of instances in the system overall, which this
reduces.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>