RTP port management
===================

This patch provides additional API capabilities for RTP
for the allocation of ports that RTP uses when creating streams.

Up to now RTP obtains a range of ports to use from its configuration
file 'rtp.conf'.  All ports were opened an all interfaces of the host.

This package allows each client channel (SIP, MGCP, H323, etc)
to select its own range of ports and allows the restriction
of binding only on the channel's own interface.

The rtp function 'ast_rtp_new' was used to open an RTP
channel pair. This has been deprecated, but is still available
for code that has not been converted to take advantage of
the new features.

The new function is 'ast_rtp_create' (as an opposite to
ast_rtp_destroy).  ast_rtp_create requires an additional
argument of *sockaddr_in which contains the IP address
information to use in binding. if the pointer to the
structure is NULL, RTP will revert to its old behavior.

It's the responsibility of the caller to setup the
structure correctly. RTP will not check the validity
of the address until it fails on bind().

If the address structure contains a non-zero port number,
RTP will try to bind to this port and if rtcp is needed,
also to port+1.  If the port was zero or cannot be
successfully bound, RTP will search in its default port
range for a successful pair.

The default port range can be overruled by the calling
channel driver with a call to 'ast_rtp_set_portrange(start,end)'
This allows each driver to use custom port ranges.

The currently installed RTP port range can be queried
with a call to 'ast_rtp_get_portrange(&start, &end)'


First implementation is for chan_sip.


khb@brose.com