Increase a maximum segment size of DMA to 4096. Previously it used

MCLBYTES for the segment size but it used too many Tx descriptors in
TSO case.
While I'm here adjust maximum size of the sum of all segment lengths
in a given DMA mapping to 65535, the maximum size, in bytes, of a IP
packet.

sys/dev/nfe/if_nfe.c

@@ -1555,9 +1555,9 @@ nfe_alloc_tx_ring(struct nfe_softc *sc, struct nfe_tx_ring *ring)
 	    BUS_SPACE_MAXADDR,
 	    BUS_SPACE_MAXADDR,
 	    NULL, NULL,
-	    MCLBYTES * NFE_MAX_SCATTER,
+	    NFE_TSO_MAXSIZE,
 	    NFE_MAX_SCATTER,
-	    MCLBYTES,
+	    NFE_TSO_MAXSGSIZE,
 	    0,
 	    NULL, NULL,
 	    &ring->tx_data_tag);

sys/dev/nfe/if_nfereg.h

@@ -50,6 +50,8 @@
 #define	NFE_JMEM	((NFE_JLEN * NFE_JSLOTS) + NFE_RESID)
 
 #define	NFE_MAX_SCATTER		32
+#define	NFE_TSO_MAXSGSIZE	4096
+#define	NFE_TSO_MAXSIZE		65535
 
 #define	NFE_IRQ_STATUS		0x000
 #define	NFE_IRQ_MASK		0x004