Do it only if a foreign master is changed to a new one,
do not do it if this is the first foreign master, i.e.
we were not synchronized to any PTP master and the clockIdentity
in the parent DS was our own. In other words, the flag
newGrandmaster is meant to detect change between foreign
masters, and not connection to a foreign master when
before there was none). The "if" was added to prevent
unnecessary trashing between SLAVE and UNCALIBRATED
state (without the if, the UNCALIBRATED would be forced
unnecesserily when connecting the link).