acm/acme.c: In show_path, fix mask for MTU, rate, and packet life time

Was using 0x1F rather than 0x3F as mask.
These fields are 6 rather than 5 bits.
More of spec conformance issue than practical issue as the
values fit into 5 bits.

Reported-by: Ilya Nelkenbaum <ilyan@mellanox.com>

Signed-off-by: Hal Rosenstock <hal@mellanox.com>