Thanks @hammer for the detailed procedure, it worked for me!
Some issues I had, hope my experience could help others who are facing the same issues:
1st I tried to enable the ssh without flashing miwifi_r3g_firmware_c2175_2.25.122.bin, I just followed the procedure to flash miwifi_ssh.bin and not only it didn’t enable SSH, but after that I tried to flash c2175_2.25.122.bin and the router stopped responding for 10 min, resetting the router (pressing the reset button while the router is on until there is a led indication) solved that issue for me.
I didn’t need to re-flash the miwifi_ssh.bin again, ssh was already enabled at that point.
The 2nd issue I faced was the router IP set to 192.168.1.1 (DHCP: 192.168.1.x) which is same as my existing router, this means I was not able to get it connected to the internet when connecting the WAN port to the LAN of my existing router.
to resolve this I had to change the mir3g default IP address, I typed the following $> vi /etc/config/network
config interface 'lan'
option ipaddr '192.168.1.1'
and changed 192.168.1.1 to 192.168.2.1 , after that I executed: $> reboot
3rd issue was the development LEDE FW does not have GUI (LUCI) installed.
to install LUCI (after I solved the DHCP issue), I followed the regular procedure:
$> opkg update
$> opkg install luci
Last issue was enabling radio0 WIFI AP (2.4GHz) on LUCI, it appears that we have to set radio0 channel to some number and not leaving it set to auto, leaving it set to auto will not allow enabling the radio0 AP. Same issue doesn’t occur with radio1 (5GHz)