selftests: drv-net: replace the rpath helper with Path objects

The single letter + "path" helpers do not have many fans (see Link).
Use a Path object with a better name. test_dir is the replacement
for rpath(), net_lib_dir is a new path of the $ksft/net/lib directory.

The Path() class overloads the "/" operator and can be cast to string
automatically, so to get a path to a file tests can do:

    path = env.test_dir / "binary"

Link: https://lore.kernel.org/CA+FuTSemTNVZ5MxXkq8T9P=DYm=nSXcJnL7CJBPZNAT_9UFisQ@mail.gmail.com
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250327222315.1098596-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/lib/py/env.py

@@ -13,23 +13,18 @@ from .remote import Remote
 class NetDrvEnvBase:
     """
     Base class for a NIC / host envirnoments
+
+    Attributes:
+      test_dir: Path to the source directory of the test
+      net_lib_dir: Path to the net/lib directory
     """
     def __init__(self, src_path):
-        self.src_path = src_path
+        self.src_path = Path(src_path)
+        self.test_dir = self.src_path.parent.resolve()
+        self.net_lib_dir = (Path(__file__).parent / "../../../../net/lib").resolve()
+
         self.env = self._load_env_file()
 
-    def rpath(self, path):
-        """
-        Get an absolute path to a file based on a path relative to the directory
-        containing the test which constructed env.
-
-        For example, if the test.py is in the same directory as
-        a binary (built from helper.c), the test can use env.rpath("helper")
-        to get the absolute path to the binary
-        """
-        src_dir = Path(self.src_path).parent.resolve()
-        return (src_dir / path).as_posix()
-
     def _load_env_file(self):
         env = os.environ.copy()