remove old kernel modules as well as kernels

sau/gentoo.py

@@ -381,6 +381,15 @@ def pkg_upgrade():
                     log.debug(f"Removing old kernel file {f}")
                     os.remove(os.path.join(root, f))
             break
+        for root, dirs, files in os.walk('/usr/lib/modules'):
+            match = sorted([d for d in dirs if re.match(r'^\d+\.\d+\.\d+-.*', d)],
+                           reverse=True,
+                           key=lambda x: tuple(map(int, x.split('-')[0].split('.')[:3])))
+            for d in match[keep_kernels:]:
+                path = os.path.join(root, d)
+                log.debug(f"Removing old modules directory {path}")
+                shutil.rmtree(path)
+            break
 
         cmd = [ GRUB_MKCONFIG, '-o', '/boot/grub/grub.cfg' ]
         ret, out, err = sau.helpers.exec_cmd(cmd)