pmc: make the TLV length a functional result.

This patch lets the TLV length field of GET messages come from a
function. For now, the function still results in a length of two,
but the intent is to allow different values later.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
pmc: send GET management messages according to interpretation #29.

This commit makes the GET messages have data bodies, just like the erratum
says to. It really doesn't make sense, but have to do it anyhow. We also
introduce a variable that will enable the legacy behavior of sending
empty bodies.

   http://standards.ieee.org/findstds/interps/1588-2008.html

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
pmc: optional legacy zero length TLV for GET actions.

This patch makes the original behavior of sending the
TLV values for GET actions with a length of zero.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
pmc_common: introduce a variable for the target port identity.

This patch replaces the hard coded wild card target port identity with
a variable initially set to the wild card value. The intent is to allow
the caller to set specific targets.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
pmc: add a command to select the target port.

This patch adds a new pmc command called "target" that lets the user
address a particular clock and port. Previously all management requests
were sent to the wild card address.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
pmc: release the message cache on exit.

This makes valgrind happier by freeing any cached message buffers.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>