sys/shell: Increase dflt max compat cmds (10->20)
sys/shell: Increase dflt max compat cmds (10->20)

This increases RAM usage by 120 bytes (10 * 12).

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core