Support size_t properties on extraInterfaces

The xyz...I2CDevice interface is needed on certain FRU object paths so
that entity-manager can know the EEPROM I2C bus and address.  It has two
size_t properties, Bus and Address.

This commit adds support for this by looking for numeric JSON properties
in the extraInterfaces JSON and saving them in the PIM payload as
size_t.

A future improvement would be to figure out the exact type needed, such
as uint64_t, int, etc.

Tested: Saw the interface on D-Bus:
xyz.openbmc_project.Inventory.Decorator.I2CDevice
.Address                                              81
.Bus                                                  30

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Iad92917b53e0dc9fdc7cd95d7452e41a8a7f6510
diff --git a/ibm_vpd_app.cpp b/ibm_vpd_app.cpp
index c6e58e6..adf68f0 100644
--- a/ibm_vpd_app.cpp
+++ b/ibm_vpd_app.cpp
@@ -311,6 +311,12 @@
                     }
                 }
             }
+            else if (itr.value().is_number())
+            {
+                // For now assume the value is a size_t.  In the future it would
+                // be nice to come up with a way to get the type from the JSON.
+                props.emplace(busProp, itr.value().get<size_t>());
+            }
         }
         interfaces.emplace(inf, move(props));
     }