Some of our files didn't have a copyright notice at all, let's add
it. Also, update the notices in other files and ensure a SPDX
identifier is present in all but the most trivial files.
Change-Id: If7fa19ce484b415bc645e39b3d0d666b44b5f0fd
According to GSM TS 04.80, table 3.4, the Return Result component
may be empty, i.e. may not contain any results nor operation code.
It is used, for example, in responce to the network-originated
USSD notification.
Change-Id: Iaaff110c5f61cc87eda6143cd841f9832f6074bf
Harald Welte
Vadim Yanitskiy