The IPv4 source routing features was removed from babeld with version
1.10. Therefore, the first_table_number option is not needed anymore and
its existance stops babeld from starting up.
As babeld 1.10 is included with OpenWrt 21.02, which is currently used
for our firmware, this option is removed.
Signed-off-by: Fabian Bläse <fabian@blaese.de>