reject: Unify inet, netdev and bridge delinearization

reject: Unify inet, netdev and bridge delinearization

Postprocessing for inet family did not attempt to kill any existing
payload dependency, although it is perfectly fine to do so. The mere
culprit is to not abbreviate default code rejects as that would drop
needed protocol info as a side-effect. Since postprocessing is then
almost identical to that of bridge and netdev families, merge them.

While being at it, extend tests/py/netdev/reject.t by a few more tests
taken from inet/reject.t so this covers icmpx rejects as well.

Cc: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Phil Sutter <phil@nwl.cc>