I noticed that in QMI wiki page 2 interface sections are created in network config.
First one is the qmi interface:
config interface 'wan' option proto 'qmi' option device '/dev/cdc-wdm0' option apn 'orange' option pincode '0000'
And a second one is defined as dhcp interface using ifname created by LTE modem.
config interface 'wwan' option ifname 'wwan0' option proto 'dhcp'
What is purpose of this second interface, as everything seems to work well without defining it.