Fix JDWP host tests on Trusty.

The buffer passed by art::JDWP::JdwpSocketState::Establish
to gethostbyname_r on Trusty was too small, leading to the
following error message during JDWP host testing:

art/runtime/jdwp/jdwp_socket.cc:283] gethostbyname_r('localhost') failed: Resolver internal error

This CL doubles the size of this buffer to avoid this
failure.

Change-Id: Ie7bb1ea8c755d869f2cc50cc2f6cc82828499706