Linux: acl_get: use "nofollow" variant of acl_extended_file call

This is NOT a bug fix, because the previous code contained a
check for symlinks before that line - because symlinks can not
have ACLs under Linux.

Now, this "is it a symlink" check is removed to simplify the
code and the "nofollow" variant of acl_extended_file* is used
to look at the symlink fs object (in the symlink case).

It then should tell us that this does NOT have an extended ACL
(because symlinks can't have ACLs) and so we return there.

Overall the code gets simpler and looks less suspect.

src/borg/platform/linux.pyx

@@ -52,7 +52,7 @@ cdef extern from "sys/acl.h":
     char *acl_to_text(acl_t acl, ssize_t *len)
 
 cdef extern from "acl/libacl.h":
-    int acl_extended_file(const char *path)
+    int acl_extended_file_nofollow(const char *path)
     int acl_extended_fd(int fd)
 
 cdef extern from "linux/fs.h":
@@ -234,17 +234,15 @@ def acl_get(path, item, st, numeric_ids=False, fd=None):
     cdef char *access_text = NULL
     cdef int ret = 0
 
-    if stat.S_ISLNK(st.st_mode):
-        # symlinks can not have ACLs
-        return
     if isinstance(path, str):
         path = os.fsencode(path)
     if fd is not None:
         ret = acl_extended_fd(fd)
     else:
-        ret = acl_extended_file(path)
+        ret = acl_extended_file_nofollow(path)
     if ret == 0:
         # there is no ACL defining permissions other than those defined by the traditional file permission bits.
+        # note: this should also be the case for symlink fs objects, as they can not have ACLs.
         return
     if ret < 0:
         raise OSError(errno.errno, os.strerror(errno.errno), os.fsdecode(path))