libfetch: Fix handling of connection failures

After commit 848f360c8f, if one tries to connect to a closed port,
fetch reports "Operation now in progress", which is rather confusing.
Return a more useful error message, restoring the old behaviour.

Fixes:		848f360c8f ("libfetch: Apply timeout to connection attempts")
Reviewed by:	des
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D58481

lib/libfetch/common.c

@@ -681,6 +681,10 @@ fetch_connect(const char *host, int port, int af, int verbose)
 					    delta.tv_usec / 1000;
 				}
 			}
+			if (pfd.revents & POLLHUP) {
+				errno = ECONNREFUSED;
+				break;
+			}
 			if (pfd.revents == POLLOUT) {
 				/* connection established */
 				err = 0;