Make sun.nio.ch.Net#connect throw ConnectException on error

openJdk7 SocketChannelImpl#connect throws SocketException when
the connect syscall fails. Pre-enso implementation thrown
ConnectException in this case. This change updates enso code
to throw the ConnectException.

Fixed #test_56684 test by trying to connect to 255.255.255.255,
which produces ENETUNREACH, like the pre-enso mock.

Bug: 25898575
Change-Id: I74212d03189a8d4a755c7cf328d5955368b32efc
3 files changed