fix capitalisation for snmp polling

[nickhilliard]

[BF] mismatch between snmp polling attributes and db column names

$SwitchPort::SNMP_MAP and $SwitchPort::OSS_SNMP_MAU_MAP were incorrectly capitalised.

Some mau* parameters pulled from snmp were not correctly cast to tinyint {0,1} before committing to DB.

In addition to the above, I have:

• [x] ensured all relevant template output is escaped to avoid XSS attached with <?= $t->ee( $data ) ?> or equivalent.
• [x] ensured appropriate checks against user privilege / resources accessed
• [x] API calls (particular for add/edit/delete/toggle) are not implemented with GET and use CSRF tokens to avoid CSRF attacks