The Buffer-to-buffer State Change Number (BB_SC_N)
field (word 1, bits 15-12) specifies the
Buffer-to-buffer State Change Number. It indicates
that the sender of the PLOGI or FLOGI frame is
requesting 2 power BB_SC_N number of frames to be
sent between two consecutive BB_SCs primitives, and
2 power BB_SC_N number of R_RDY primitives to be
sent between two consecutive BB_SCr primitives.
If 'true', the BB_SC_N mode is enabled.
If 'false', the BB_SC_N mode is disabled.