[infiniband] Centralise assumption of 2048-byte payloads

IPoIB and the SMA have separate constants for the packet size to be
used to I/O buffer allocations.  Merge these into the single
IB_MAX_PAYLOAD_SIZE constant.

(Various other points in the Infiniband stack have hard-coded
assumptions of a 2048-byte payload; we don't currently support
variable MTUs.)

src/include/gpxe/ib_qset.h

@@ -20,16 +20,13 @@ struct ib_queue_set {
 	struct ib_queue_pair *qp;
 	/** Receive work queue maximum fill level */
 	unsigned int recv_max_fill;
-	/** Receive packet length */
-	size_t recv_pkt_len;
 };
 
 extern int ib_create_qset ( struct ib_device *ibdev,
 			    struct ib_queue_set *qset, unsigned int num_cqes,
 			    struct ib_completion_queue_operations *cq_op,
 			    unsigned int num_send_wqes,
-			    unsigned int num_recv_wqes, size_t recv_pkt_len,
-			    unsigned long qkey );
+			    unsigned int num_recv_wqes, unsigned long qkey );
 extern void ib_qset_refill_recv ( struct ib_device *ibdev,
 				  struct ib_queue_set *qset );
 extern void ib_destroy_qset ( struct ib_device *ibdev,

src/include/gpxe/ib_sma.h

@@ -37,9 +37,6 @@ struct ib_sma {
 	struct process poll;
 };
 
-/** SMA payload size allocated for received packets */
-#define IB_SMA_PAYLOAD_LEN 2048
-
 /** SMA number of send WQEs
  *
  * This is a policy decision.

src/include/gpxe/infiniband.h

@@ -24,6 +24,14 @@ FILE_LICENCE ( GPL2_OR_LATER );
 /** Subnet administrator queue key */
 #define IB_GLOBAL_QKEY 0x80010000UL
 
+/**
+ * Maximum payload size
+ *
+ * This is currently hard-coded in various places (drivers, subnet
+ * management agent, etc.) to 2048.
+ */
+#define IB_MAX_PAYLOAD_SIZE 2048
+
 struct ib_device;
 struct ib_queue_pair;
 struct ib_address_vector;

src/include/gpxe/ipoib.h

@@ -10,9 +10,6 @@ FILE_LICENCE ( GPL2_OR_LATER );
 
 #include <gpxe/infiniband.h>
 
-/** IPoIB packet length */
-#define IPOIB_PKT_LEN 2048
-
 /** IPoIB MAC address length */
 #define IPOIB_ALEN 20