Remove "Static" keyword from pipex(4) layer.

Remove "Static" keyword from pipex(4) layer.

We don't use "static" keyword for functions declaration to allow ddb(4)
debug. Also, many "Static" functions are called by pppx(4) layer outside
pipex(4) layer.

This is the mostly mechanic diff, except the `pipex_pppoe_padding' which
should be "static const".

ok bluhm@ yasuoka@