[starnix][fastrpc] Initialize Vec with_capacity.

Change-Id: Ic6544056e08691bcde7bab756a6e0b8b84a601f4
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1573333
Reviewed-by: Benjamin Lerman <qsr@google.com>
Commit-Queue: Nelly Vouzoukidou <nellyv@google.com>
1 file changed