XEP-0198: Change state on gen_tcp:send/2 failure

When Stream Management is enabled and a gen_tcp:send/2 call fails, go
into the 'wait_for_resume' state immediately.  This makes sure that
gen_tcp:send/2 won't be called again, which might avoid an Erlang issue
where gen_tcp:send/2 apparently hangs despite 'send_timeout' (and
'send_timeout_close') being set.