i2pd: Update to 2.29.0

Ran init script through shellcheck. Simplified several statements.

Replaced INSTALL_CONF with INSTALL_DATA. i2pd runs as non-root and so the
conf file must be accessible.

Fixed: https://github.com/openwrt/packages/issues/10977



Signed-off-by: Rosen Penev <rosenp@gmail.com>