nut: fix other/otherflag custom variables in nut-server.init

This allows custom config parameters to be added to the generated config
files, enabling the original intended functionality per
https://openwrt.org/docs/guide-user/services/ups/software.nut

.

Example usage from /etc/config/nut_server:

config driver 'apc'
	option driver 'snmp-ups'
	option snmp_version 'v3'
	option port '172.16.100.5'
	list other 'secLevel'
	list other 'secName'
	list other 'authPassword'
	list otherflag 'notransferoids'

config other 'other_secLevel'
	option value 'authNoPriv'

config other 'other_secName'
	option value 'some_username'

config other 'other_authPassword'
	option value 'some_password'

config other 'otherflag_notransferoids'
	option value '1'

Signed-off-by: Matt Merhar <mattmerhar@protonmail.com>