The driver no longer collects over SNMP. SNMP_HEALTH_PROFILE states
where the switch publishes its values; the application polls and
computes (napalm-device-types docs/STRUCTURE.md).
This also fixes the memory figure: NETSWITCH-MIB hpLocalMemEntry column
6 is free memory, not used. On swt-l0-3-40 total 58720256 = free
39105640 + allocated 19614616, so the switch showed 66.6 % used instead
of 33.4 %. The profile names column 6 as free.
Interface counters now come from the 64-bit ifXTable where the switch
has it, as the application reads them for every device.
Closes#9
