unicast_rtp_request() was setting the channel variables like this:
pbx_builtin_setvar_helper(chan, "UNICASTRTP_LOCAL_ADDRESS",
ast_sockaddr_stringify_addr(&local_address));
ast_rtp_instance_get_local_address(instance, &local_address);
pbx_builtin_setvar_helper(chan, "UNICASTRTP_LOCAL_PORT",
ast_sockaddr_stringify_port(&local_address));
...which made it appear that UNICASTRTP_LOCAL_ADDRESS was being
set before local_address was set. In fact, the address part of
local_address was set earlier in the function, just not the port.
This was confusing however so ast_rtp_instance_get_local_address()
is now being called before setting UNICASTRTP_LOCAL_ADDRESS.
ASTERISK-30281
Change-Id: I872ac49477100f4eb33891d46efc6ca21ec81aa4
9de862242f