Allow binding to a random port.

In TCP, binding to port 0 means asking the OS to choose an available
ephemeral port to bind to. In this case, network-transport-tcp
erroneously thinks the address is then "host:0", which has no meaning to
any peer.

This patch fixes the situation, by querying what port was obtained from
the OS before constructing the endpoint address.
Allow network 2.5 and 2.6
.gitignore.
Merge pull request #4 from tweag/master

Bump upper bound on network-transport-tests.
Merge pull request #3 from tweag/fix-zero-port-patch

Allow binding to a random port. Thanks @qnikst
Merge branch 'network-vsn-fix'

* network-vsn-fix:
  Allow network 2.5 and 2.6

Conflicts:
	network-transport-tcp.cabal