libprocstat: copy all the 32-bit auxv entries

Use source struct size not the destination struct size so we copy all
the auxv entries, not just the first half of them.

Fix a style issue on an adjacent line.

Reviewed by: markj
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D42200

(cherry picked from commit 8f06fabe39ac3ebca4ab448a456945008305a23f)