um,ethertap: use strncpy

[um maintainers appear to be vanished]

I can't prove the case pointed out in
https://bugzilla.kernel.org/show_bug.cgi?id=82341
is correct so let us play safe.

Signed-off-by: Alan Cox <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

arch/um/os-Linux/drivers/ethertap_user.c

···
 	sprintf(data_fd_buf, "%d", data_remote);
 	sprintf(version_buf, "%d", UML_NET_VERSION);
 	if (gate != NULL) {
-		strcpy(gate_buf, gate);
+		strncpy(gate_buf, gate, 15);
 		args = setup_args;
 	}
 	else args = nosetup_args;