Argument improvements, cosmetic changes

[boksanns94]

Hey Werner,
I found your script very useful for monitoring synology devices. Wanted to suggest changes that would make running the script more modular.

CHANGES:

• Changed some arguments to make them all optional and keyword arguments, since (in my case) we have a bunch of synology devices and there are different confiurations among them (regarding privacy being enabled or not, different ports, usernames, passwords etc.)
• Did cosmetic changes. Made script more compliant with PEP8 and implemented f-string formatting instead of concatenation and format-strings.
• Moved "ExitCode" function so its declared before it is used.
• Renamed "snmpget" and "snmpwalk" to "snmp_get" and "snmp_walk".
• Added spaces around math symbols (+, /, etc.)

These are the things I changed.
Regads