Inject debug spikes ICSHWI-10474

Adds a patch which allows for injecting artificial offsets into the NTP SHM for debugging purposes. We have seen that a large offset between EVR time and System time in the NTP SHM (which can occur after restart or even possibly randomly due to thread execution being delayed)

The variables:

• ntpShmDebugInjectSpike
• ntpShmDebugSpikeLength
• ntpShmDebugSpikeOffsetNS

Usage from iocsh

# Configure an extra, artificial offset to be added to the system (receive) time 
# written to the NTP SHM by time2ntp of MRFIOC2.
 
# Set the extra offset to be 0.5 seconds last for 10 updates (seconds)
var ntpShmDebugSpikeOffsetNS 500000000
var ntpShmDebugSpikeLength 10

# Trigger the spike
var ntpShmDebugInjectSpike 1