selftests/net: add nettest to .gitignore

nettest is missing from gitignore.

Fixes: acda655 ("selftests: Add nettest")
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Jakub Kicinski

tools/testing/selftests/net/.gitignore

@@ -21,3 +21,4 @@ ipv6_flowlabel
 ipv6_flowlabel_mgr
 so_txtime
 tcp_fastopen_backup_key
+nettest