MEDIUM: stream: only loop on flags relevant to the analysers

MEDIUM: stream: only loop on flags relevant to the analysers

In process_stream() we detect a number of conditions to decide to loop
back to the analysers. Some of them are excessive in that they perform
a strict comparison instead of filtering on the flags relevant to the
analysers as is done at other places, resulting in excess wakeups. One
of the effect is that after a successful WRITE_PARTIAL, a second send is
not possible, resulting in the loss of WRITE_PARTIAL, causing another
wakeup! Let's apply the same mask and verify the flags correctly.