selftests/net: unix: fix unused variable compiler warning

Remove an unused variable.

diag_uid.c:151:24:
error: unused variable 'udr'
[-Werror,-Wunused-variable]

Fixes: ac011361bd4f ("af_unix: Add test for sock_diag and UDIAG_SHOW_UID.")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20231124171645.1011043-4-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

af_unix: Add test for sock_diag and UDIAG_SHOW_UID.

The test prog dumps a single AF_UNIX socket's UID with and without
unshare(CLONE_NEWUSER) and checks if it matches the result of getuid().

Without the preceding patch, the test prog is killed by a NULL deref
in sk_diag_dump_uid().

# ./diag_uid
TAP version 13
1..2
# Starting 2 tests from 3 test cases.
# RUN diag_uid.uid.1 ...
BUG: kernel NULL pointer dereference, address: 0000000000000270
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 105212067 P4D 105212067 PUD 1051fe067 PMD 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.amzn2022.0.1 04/01/2014
RIP: 0010:sk_diag_fill (./include/net/sock.h:920 net/unix/diag.c:119 net/unix/diag.c:170)
...
# 1: Test terminated unexpectedly by signal 9
# FAIL diag_uid.uid.1
not ok 1 diag_uid.uid.1
# RUN diag_uid.uid_unshare.1 ...
# 1: Test terminated by timeout
# FAIL diag_uid.uid_unshare.1
not ok 2 diag_uid.uid_unshare.1
# FAILED: 0 / 2 tests passed.
# Totals: pass:0 fail:2 xfail:0 xpass:0 skip:0 error:0

With the patch, the test succeeds.

# ./diag_uid
TAP version 13
1..2
# Starting 2 tests from 3 test cases.
# RUN diag_uid.uid.1 ...
# OK diag_uid.uid.1
ok 1 diag_uid.uid.1
# RUN diag_uid.uid_unshare.1 ...
# OK diag_uid.uid_unshare.1
ok 2 diag_uid.uid_unshare.1
# PASSED: 2 / 2 tests passed.
# Totals: pass:2 fail:0 xfail:0 xpass:0 skip:0 error:0

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>