PSA Restrictions on type H?

[jafingerhut]

Some combination of p4c and BMv2 simple_switch impose the restriction that for P4_16 plus the v1model architecture, type parameter H must be a struct that contains only members with type header, header stack, and/or header_union.

Perhaps the same restriction should apply for PSA type parameters that represent collections of headers?

p4lang/behavioral-model#701
p4lang/p4c#1676

[jafingerhut]

Created a PR intended to address this issue: #1027