[lwip-devel] C++ style comments

[Kieran Mansley]

A few changes have gone in recently that included C++ style (i.e. "//"
rather than "/* */") comments.  This is normally harmless but our unix
ports have the pedantic gcc flag set for compilation, and so complain
about this.  I've fixed the ones I've found but if we could avoid them
it would save me a little time.

Thanks!

Kieran