Add API to register callback to set socket options

The registered callback function will be called before connect() is
called on the socket, allowing tweaking of much more than just keepalive
settings.

This deprecates xmpp_conn_set_keepalive().

Includes helper/example callback function to set default keepalive
parameters that some library users may find useful.

src/sock.h

@@ -22,6 +22,9 @@
 typedef int sock_t;
 #else
 #include <winsock2.h>
+#include <ws2tcpip.h>
+#include <iphlpapi.h>
+#include <mstcpip.h> /* tcp_keepalive */
 typedef SOCKET sock_t;
 #endif
 
@@ -30,7 +33,7 @@ void sock_shutdown(void);
 
 int sock_error(void);
 
-sock_t sock_connect(const char *host, unsigned short port);
+sock_t sock_connect(xmpp_conn_t *conn, const char *host, unsigned short port);
 int sock_close(sock_t sock);
 
 int sock_set_blocking(sock_t sock);
@@ -40,6 +43,10 @@ int sock_write(sock_t sock, const void *buff, size_t len);
 int sock_is_recoverable(int error);
 /* checks for an error after connect, return 0 if connect successful */
 int sock_connect_error(sock_t sock);
-int sock_set_keepalive(sock_t sock, int timeout, int interval);
+int sock_set_keepalive(sock_t sock,
+                       int timeout,
+                       int interval,
+                       int count,
+                       unsigned int user_timeout);
 
 #endif /* __LIBSTROPHE_SOCK_H__ */