Fix for pr2837451.
Fix for pr2837451.

pr2827132 changed the val_ field in vvp_fun_part_sa to only store
the bit values for the selected part, not the entire source vector,
but omitted to modify the recv_vec4_pv method to handle this change.
This patch rectifies that omission.

CastMi/iverilog,themperek/iverilog,CastMi/iverilog,CastMi/iverilog,themperek/iverilog,themperek/iverilog