Quagga has no snmp support, unrecognized options --enable-tcp-md5

1. Quagga's tcp-md5 has been renamed to linux24-tcp-md5

2. net-snmp needs to have mib-modules=smux enabled to enable
quagga to support snmp. Make the net-snmp option dependent
on the DISTRO_FEATURE snmp.

3. Misc: install the sample conf files for quagga. Also,
Make sure that the post install script is being run
on the target rather than during the rootfs creation
stage.

Signed-off-by: Amy Fong <amy.fong@windriver.com>
Signed-off-by: Aws Ismail <aws.ismail@windriver.com>
Signed-off-by: Joe MacDonald <joe.macdonald@windriver.com>