add option to listen on loopback only

[wydrych]

scope

Use -O to listen on loopback only – with keeping AFI selection by -4 / -6.

I guess it would be more valuable to add option to define listening address, but for my use-case listening on any vs loopback is enough and I see this patch as a good start.

verification

I expect no behavior change if sflowtool is run w/o -O. Output of netstat -anpl | fgrep sflow is attached for verification.

listening on any

sflowtool

udp6       0      0 :::6343                 :::*                                1629540/src/sflowto 

sflowtool -4

udp        0      0 0.0.0.0:6343            0.0.0.0:*                           1629694/src/sflowto 

sflowtool -6

udp6       0      0 :::6343                 :::*                                1629769/src/sflowto 

listening on loopback only

sflowtool -O

udp6       0      0 ::1:6343                :::*                                1629842/src/sflowto 

sflowtool -4 -O (or -4O)

udp        0      0 127.0.0.1:6343          0.0.0.0:*                           1629864/src/sflowto 

sflowtool -6 -O (or -6O)

udp6       0      0 ::1:6343                :::*                                1629905/src/sflowto 

[sflow]

I think specifying a bind address, or interface, might be the way to go.

[wydrych]

I think specifying a bind address, or interface, might be the way to go.

The former hasn't taken too much time, see #45 :-) (And should you prefer #45, we can close #44 w/o merging.)