GD-Packet: Increase sharding number to 10

* Increase packet source sharding from 5 to 10 to better utilize
  parallelism on workstations during compilation
* Reduces compilation time by about 35%

Test: gd/cert/run --host
Tag: #gd-refactor
Change-Id: I44e13545e812ad9b165f40f349601f20b6b7bee9