Prepare the relevant part of the diff for some tests
'''
$ cat > t
_icmp_drop_redirect="${icmp_drop_redirect}"
case "${_icmp_drop_redirect}" in
[Aa][Uu][Tt][Oo] | "")
_icmp_drop_redirect="${routed_enable}"
;;
esac
'''
Test "auto" values:
'''
$ icmp_drop_redirect="auto"
$ routed_enable="no"
$ . t
$ set | grep _
_icmp_drop_redirect=no
icmp_drop_redirect=auto
routed_enable=no
'''
'''
$ routed_enable="yes"
$ . t
$ set | grep _
_icmp_drop_redirect=yes
icmp_drop_redirect=auto
routed_enable=yes
'''
Overwrite the router setting:
'''
$ routed_enable="yes"
$ icmp_drop_redirect="no"
$ . t
$ set | grep _
_icmp_drop_redirect=no
icmp_drop_redirect=no
routed_enable=yes
'''
'''
$ icmp_drop_redirect="yes"
$ . t
$ set | grep _
_icmp_drop_redirect=yes
icmp_drop_redirect=yes
routed_enable=yes
'''