selftests: net: add netlink-dumps to .gitignore

Commit 55d42a0c3f ("selftests: net: add a test for closing
a netlink socket ith dump in progress") added a new test
but did not add it to gitignore.

Reviewed-by: Joe Damato <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

tools/testing/selftests/net/.gitignore

@@ -19,6 +19,7 @@ log.txt
 msg_oob
 msg_zerocopy
 ncdevmem
+netlink-dumps
 nettest
 psock_fanout
 psock_snd