Add missing nil check for DPC when processing wwan status update

DPC can be still nil when DPCManager receives the first status from
the wwan microservice. Without nil check, processWwanStatus function
may therefore hit the nil dereference panic.

Another small change in this commit is to avoid redundant calls
to currentDPC() - dpc is already retrieved at the beginning of the
function.

Signed-off-by: Milan Lenco <[email protected]>
(cherry picked from commit a984bcb)

pkg/pillar/dpcmanager/wwan.go

@@ -76,14 +76,14 @@ func (m *DpcManager) processWwanStatus(ctx context.Context, status types.WwanSta
 	}
 
 	if changed || wasInProgress {
-		if m.currentDPC() != nil {
-			changedDPC := m.setDiscoveredWwanIfNames(m.currentDPC())
+		if dpc != nil {
+			changedDPC := m.setDiscoveredWwanIfNames(dpc)
 			if changedDPC {
 				m.publishDPCL()
 			}
 		}
 		m.updateDNS()
-		if dpc.State == types.DPCStateWwanWait {
+		if dpc != nil && dpc.State == types.DPCStateWwanWait {
 			m.runVerify(ctx, "wwan status is up-to-date")
 		} else {
 			m.restartVerify(ctx, "wwan status changed")