libwebsockets

ss: make sure to use LWS_WRITE_HTTP_FINAL with SS EOM flag

When most of ss-h2 was combined into ss-h1 during development, the h2 difference
about needing HTTP_FINAL to signal h2 FIN flag was accidentally dropped.  In
many cases the peer can infer it, from, eg, content-length reached.  But we need
to replace explicitly doing it to cover all cases.