At a quick glance it looks like using socket_workers when the listen parameter uses the interface name does not work.  For example:

children = 4

socket_workers=2

listen=udp:10.10.10.10:5060

Gives two listeners on udp:10.10.10.10:5060

children = 4

socket_workers=2

listen=udp:eth0:5060

Gives four listeners on the socket.

Note this is just a quick cursory observation.  Is it by design or a design limitation?

Kaufman