nimble/ll: Allow 2M params as fallback for ext conn create

We ignore 2M values only for scanning since we do not scan on 2M when
ext conn create is pending, but there's nothing wrong in using those
parameters as fallback in case we established connection on phy that
was not in phy mask.

nimble/controller/src/ble_ll_conn_hci.c

@@ -707,6 +707,9 @@ ble_ll_ext_conn_create(const uint8_t *cmdbuf, uint8_t len)
         ble_ll_conn_itvl_to_ticks(conn_itvl_max, &hcc.params[1].conn_itvl_ticks,
                                   &hcc.params[1].conn_itvl_usecs);
 
+        if (!fallback_params) {
+            fallback_params = &hcc.params[1];
+        }
         params++;
     }
 #endif