Extend the dynamic update protocol to expose the pif indices and names
from a running passt/pasta to the pesto tool.  pesto records that data
and prints it out.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
[sbrivio: In read_pif_conf(), force a redundant termination of the
 interface name, the existing check isn't obvious enough for static
 checkers]
[sbrivio: Drop @resv_ left-over in description of struct
 pesto_pif_info, reported by Jon Maloy]
[sbrivio: Fix minor nits reported by Laurent]
[sbrivio: Initialise struct pesto_pif_info in conf_send_rules() with
 zeroes, otherwise the pif name might be seen as not terminated, and
 we'll expose memory from the back-end]
[sbrivio: Fix conflicts in Makefile]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Add helpers to serialise/deserialise unsigned integers, handling endian
conversion so that the stream format is consistent regardless of host
endiannness.  Currently we only use this on one place: sending the number
of flows during migration.  We're going to have more use for this as we
add dynamic configuration updates, so these will become more useful.

For now we only need a 32-bit version, however define the functions with
a macro so we can easily add other integer widths when we need them.

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

The read_all_buf() and write_all_buf() functions in util.c are
primarily used for serialising data structures to a stream during
migraiton.  We're going to have further use for such serialisation
when we add dynamic configuration updates, where we'll want to share
the code with the client program.

To make that easier move the functions into a new serialise.c
file, and rename thematically.

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