This determines the frame types that will be blocked
for this protocol class on this TrCRF on this port. Setting
the values causes the following:
all(1) - causes all frames in this class to be blocked
sr(2) - causes source route frames in this class to
be blocked
nsr(3) - causes non source routed frames in this class
to be blocked
none(4) - allow all frames in this protocol class. This
is the default value.