Propagate kwargs in mb.load when backend is gmso. Fix #1034 (#1035)

* Propagate kwargs in mb.load when backend is gmso. Fix #1034

* Fix failed test
Parmed don't have support for reading in "lj" type mol2, so removing
that kwarg from the load using parmed as backend

Co-authored-by: Co Quach <43968221+daico007@users.noreply.github.com>
Co-authored-by: Co Quach <daico007@gmail.com>

mbuild/conversion.py

@@ -428,7 +428,7 @@ def load_file(
     if backend == "gmso":
         gmso = import_("gmso")
 
-        top = gmso.Topology.load(filename=filename)
+        top = gmso.Topology.load(filename=filename, **kwargs)
         compound = from_gmso(
             topology=top,
             compound=compound,

mbuild/tests/test_mol2file.py

@@ -33,3 +33,20 @@ def test_gmso_backend(self):
         for particle in gmso_silica_surface:
             element_set.add(particle.element)
         assert len(element_set) == 2
+
+    def test_gmso_backend_lj_site_type(self):
+        pmd_silica_surface = mb.load(
+            filename_or_object=get_fn("beta-cristobalite-expanded.mol2"),
+            backend="parmed",
+        )
+        gmso_silica_surface = mb.load(
+            filename_or_object=get_fn("beta-cristobalite-expanded.mol2"),
+            backend="gmso",
+            site_type="lj",
+        )
+
+        assert pmd_silica_surface.n_particles == gmso_silica_surface.n_particles
+        assert pmd_silica_surface.n_bonds == gmso_silica_surface.n_bonds
+
+        for particle in gmso_silica_surface:
+            assert particle.element is None