convert bytefields in common to usable fields

[nopeslide]

Instead of having a handy way to quickly instantiate the various protocols in common as standalone bytefield,
lets make them fields, that can be used in other bytefields.
these fields may allow their internal fields to be overwritten via arguments

#bytefield(
  ip(
    data: tcp(
      dst_port: [80] // set internal field content 
      src_port: bytes(2)[#box(width:100%,height:100%,fill:grey)[random]] //replace internal field
    )[
      GET ...
    ]
  )
)

[jomaway]

Sounds like a good idea.
But maybe we can even support both versions like common.ipv4 just stays like it is and common.fields.ipv4 returns the field or something similar.

Happy to accept a PR if you like to implement this. Otherwise i put it on the list for future plans.