osmo-bts-trx: Enable osmotrx tx-attenuation oml by default

There are currently two ways to specify power reductions to be sent to
osmo-trx from osmo-bts-trx:
* osmotrx tx-attenuation oml
* osmotrx tx-attenuation <0-50>

None of them is enabled by default, which means if none of them is
specified in the config file of osmo-bts-trx, SETPOWER cmd won't be sent
to osmo-trx, which in turn won't turn on the transciever.

Let's enable osmo tx-attenuation oml by default and leave it up to the
bsc to decide which power reduction to use. If the user wants to
configure a specific tx-attentuation, it can still do so in exactly the
same way he used to do it.

Change-Id: Ia8640751630ee37e5f5d1f470bad892a08e80654

src/osmo-bts-trx/main.c

@@ -130,6 +130,8 @@ void bts_model_phy_instance_set_defaults(struct phy_instance *pinst)
 	l1h = talloc_zero(tall_bts_ctx, struct trx_l1h);
 	l1h->phy_inst = pinst;
 	pinst->u.osmotrx.hdl = l1h;
+
+	l1h->config.power_oml = 1;
 }
 
 int main(int argc, char **argv)