remove a questional error handling

as our underlying transport (tcp/ssl) is a stream which doesn't preserve
message boundaries, dropping an unparsable segment likely make the
situation worse.
fix message header parsing

if not enough bytes of data are available, return {error, binary_too_small}
so that the caller can retry when more data come.  it's normal as
our underlying transport (tcp etc) does not preserve message boundaries.
Fix value of OFPG_MAX

This constant was introduced with the value 0xffffff00 in version 1.3.1
of the spec.  Fix our macro to use the correct value.

Motivated by FlowForwarding/LINC-Switch#191.
Fix typo in type name ofp_group_mod_failed
fix some of ofp_v4 table_feature_prop_type constants
Merge pull request #50 from legoscia/fix-OFPG_MAX

Fix value of OFPG_MAX
Merge pull request #56 from yamt/fix-table-feature-req

fix some of ofp_v4 table_feature_prop_type constants
Add unit tests for ofp_parser

We should also test parsing fragments smaller than 8 bytes: see
FlowForwarding/of_protocol#40.
Merge branch 'fix-parser' of github.com:yamt/of_protocol into yamt-fix-parser
Add unit test for parsing 7 byte fragments

This now works!