main/dropbear: enable ssh config
The "per-client config file" feature needs to be compiled with DROPBEAR_USE_SSH_CONFIG=1
(https://github.com/mkj/dropbear/pull/216)
The "per-client config file" feature needs to be compiled with DROPBEAR_USE_SSH_CONFIG=1
(https://github.com/mkj/dropbear/pull/216)