Vararg functions have a different calling convention than regular
functions on amd64. Casting a varag function to a regular one to
match the function pointer declaration will hide the varargs from
the caller and we will end up with an incorrectly setup stack.
Entirely remove the varargs from these functions and change the
functions to match the declaration of the function pointers.
Remove the now unnecessary casts.
Also change static struct ipprotosw[] to two independent
protosw/ip6protosw definitions to remove an unnecessary cast.
PR: amd64/95008
Submitted and tested by: Mats Palmgren
Reviewed by: rwatson
MFC after: 3 days
e59d4d98ef