agent lld items return formatted json

for some reason zabbix agent returns formatted/indented json for discovery items. that doesn't seem to be needed, increases the amount transmitted and also the amount stored on proxies, for example.

let's consider net.if.discovery that would return data for 3 entities lo/eth0/eth1

returned json is :

{
        "data":[
                {
                        "{#IFNAME}":"lo"},
                {
                        "{#IFNAME}":"eth0"},
                {
                        "{#IFNAME}":"eth1"}]}

unless i messed up counting, that's 71 meaningful bytes and 24 tabs & newlines, which is some 34% of data on top of the meaningful size.

probably all whitespace should be discarded (or not added in the first place )