Function silc_packet_send_prepare
SYNOPSIS
void silc_packet_send_prepare(SilcSocketConnection sock,
uint32 header_len,
uint32 padlen,
uint32 data_len);
DESCRIPTION
Prepare outgoing data buffer for packet sending. This moves the data
area so that new packet may be added into it. If needed this allocates
more space to the buffer. This handles directly the connection's
outgoing buffer in SilcSocketConnection object.