netmonitor: timeout calling dhcpcd executable

Add a timeout when calling dhcpcd in case it hangs; this
prevents the whole DPCManager from hanging and ultimatevely
making the watchdog fire and reboot the system.

Signed-off-by: Christoph Ostarek <[email protected]>
(cherry picked from commit e628c59)

Author: christoph-zededa

pkg/pillar/netmonitor/linux.go

@@ -257,7 +257,7 @@ func (m *LinuxNetworkMonitor) GetInterfaceDHCPInfo(ifIndex int) (info DHCPInfo,
 	// XXX Getting error -1 unless we add argument -4.
 	// XXX Add IPv6 support.
 	m.Log.Functionf("Calling dhcpcd -U -4 %s\n", ifName)
-	stdoutStderr, err := base.Exec(m.Log, "dhcpcd", "-U", "-4", ifName).CombinedOutput()
+	stdoutStderr, err := base.Exec(m.Log, "dhcpcd", "-U", "-4", ifName).CombinedOutputWithTimeout()
 	if err != nil {
 		if strings.Contains(string(stdoutStderr), "dhcp_dump: No such file or directory") {
 			// DHCP is not configured for this interface. Return empty DHCPInfo.