build-sys: rename project to libslirp

Let's follow gitlab project name.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
diff --git a/meson.build b/meson.build
index 287802b..94578dc 100644
--- a/meson.build
+++ b/meson.build
@@ -1,4 +1,4 @@
-project('slirp', 'c',
+project('libslirp', 'c',
   version : '4.0.0',
   license : 'BSD-3-Clause',
   default_options : ['warning_level=1', 'c_std=gnu99']