drbd: add missing drbd command names to avoid <NULL> in error messages

cmdname() should map command number to its human readable
representation. The string table was incomplete, though.

Maybe rather do a switch() block, and let the compiler help us
to keep it complete?
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_int.h

@@ -261,6 +261,9 @@ static inline const char *cmdname(enum drbd_packets cmd)
 		[P_OV_REQUEST]          = "OVRequest",
 		[P_OV_REPLY]            = "OVReply",
 		[P_OV_RESULT]           = "OVResult",
+		[P_CSUM_RS_REQUEST]     = "CsumRSRequest",
+		[P_RS_IS_IN_SYNC]	= "CsumRSIsInSync",
+		[P_COMPRESSED_BITMAP]   = "CBitmap",
 		[P_MAX_CMD]	        = NULL,
 	};