MEDIUM: log-format: backend source address %Bi %Bp

%Bi return the backend source IP
%Bp return the backend source port

Add a function pointer in logformat_type to do additional configuration
during the log-format variable parsing.
diff --git a/include/types/proxy.h b/include/types/proxy.h
index 6693d82..26cdfe4 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -138,7 +138,9 @@
 #define PR_O2_NODELAY   0x00020000      /* fully interactive mode, never delay outgoing data */
 #define PR_O2_USE_PXHDR 0x00040000      /* use Proxy-Connection for proxy requests */
 #define PR_O2_CHK_SNDST 0x00080000      /* send the state of each server along with HTTP health checks */
-/* unused: 0x00100000 */
+
+#define PR_O2_SRC_ADDR	0x00100000	/* get the source ip and port for logs */
+
 #define PR_O2_FAKE_KA   0x00200000      /* pretend we do keep-alive with server eventhough we close */
 /* unused: 0x00400000 */
 #define PR_O2_EXP_NONE  0x00000000      /* http-check : no expect rule */