flow: Record the pifs for each side of each flow

Currently we have no generic information flows apart from the type and
state, everything else is specific to the flow type.  Start introducing
generic flow information by recording the pifs which the flow connects.

To keep track of what information is valid, introduce new flow states:
INI for when the initiating side information is complete, and TGT for
when both sides information is complete, but we haven't chosen the
flow type yet.  For now, these states don't do an awful lot, but
they'll become more important as we add more generic information.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

pif.h

@@ -38,7 +38,6 @@ static inline const char *pif_type(enum pif_type pt)
 		return "?";
 }
 
-/* cppcheck-suppress unusedFunction */
 static inline const char *pif_name(uint8_t pif)
 {
 	return pif_type(pif);