MINOR: raw_sock: always report asynchronous connection errors

MINOR: raw_sock: always report asynchronous connection errors

Depending on the pollers used, a connection error may be notified
with POLLOUT|POLLERR|POLLHUP. POLLHUP by itself is enough for the
connection handler to call the read actor, which would only consider
this flag as a good indication of a hangup, without considering the
POLLERR flag.

In order to address this, we directly jump to the read0 label if
POLLERR was not set.

This will be important with health checks as we don't want to believe
a connection was properly established when it's not the case !