Applies only to X25 PVCs and DLM circuits. Specifies the maximum
 packet size for the X25 circuit. This value must be at least five
 bytes less than the MAXIMUM BLOCK value that you specify in the SET or
 DEFINE LINE command, and must be a power of two. Specify a value in
 the range 16 to 4096 bytes.

 By default, packet size takes the value specified by the PROFILE
 parameter of the SET or DEFINE MODULE X25-PROTOCOL command.