unix: fix Listen on solaris

libsocket has __xnet_listen, not __xnet_llisten
which prevents listen from working.

Change-Id: Ia06dc569fcb9950893d91fc1b86257c7742e9e3d
GitHub-Last-Rev: 6f37c4b81409db28f20c2acfbd5ccae9cdb2b510
GitHub-Pull-Request: golang/sys#258
Reviewed-on: https://go-review.googlesource.com/c/sys/+/691735
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Jes Cok <xigua67damn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>