pyloxi: move OFType interface functions to module level

This removes the need to replace the LOXI IR OFType object in members with our
own version. If/when the core OFType is upgraded to an inheritance hierachy we
won't need to duplicate it in pyloxi.
diff --git a/py_gen/templates/_pretty_print.py b/py_gen/templates/_pretty_print.py
index 65c5941..7be7a14 100644
--- a/py_gen/templates/_pretty_print.py
+++ b/py_gen/templates/_pretty_print.py
@@ -44,15 +44,15 @@
                     q.text("%#x" % self.${m.name})
                 else:
                     q.text('None')
-:: elif m.oftype.base == 'of_mac_addr_t':
+:: elif m.oftype == 'of_mac_addr_t':
                 q.text(util.pretty_mac(self.${m.name}))
-:: elif m.oftype.base == 'uint32_t' and m.name.startswith("ipv4"):
+:: elif m.oftype == 'uint32_t' and m.name.startswith("ipv4"):
                 q.text(util.pretty_ipv4(self.${m.name}))
-:: elif m.oftype.base == 'of_wc_bmap_t' and version in [1,2]:
+:: elif m.oftype == 'of_wc_bmap_t' and version in [1,2]:
                 q.text(util.pretty_wildcards(self.${m.name}))
-:: elif m.oftype.base == 'of_port_no_t':
+:: elif m.oftype == 'of_port_no_t':
                 q.text(util.pretty_port(self.${m.name}))
-:: elif m.oftype.base.startswith("uint"):
+:: elif m.oftype.startswith("uint"):
                 q.text("%#x" % self.${m.name})
 :: else:
                 q.pp(self.${m.name})