[hermon] Reduce the RC ACK timeout

The ACK timeout determines how long we take to notice a failed
Reliable Connection.  Reducing it from the arbitrary value of 19 down
to 14 reduces the individual ACK timeout from around 2.1s to 67ms;
this in turn reduces the time to tear down and re-establish a broken
SRP session from around 30s to around 1s.

src/drivers/infiniband/hermon.c

 		memset ( &qpctx, 0, sizeof ( qpctx ) );
 		MLX_FILL_1 ( &qpctx, 10,
 			     qpc_eec_data.primary_address_path.ack_timeout,
-			     0x13 );
+			     14 /* 4.096us * 2^(14) = 67ms */ );
 		MLX_FILL_2 ( &qpctx, 30,
 			     qpc_eec_data.retry_count, HERMON_RETRY_MAX,
 			     qpc_eec_data.rnr_retry, HERMON_RETRY_MAX );