uapi: fix linux/rds.h userspace compilation errors

Consistently use types from linux/types.h to fix the following
linux/rds.h userspace compilation errors:

/usr/include/linux/rds.h:198:2: error: unknown type name 'u8'
  u8 rx_traces;
/usr/include/linux/rds.h:199:2: error: unknown type name 'u8'
  u8 rx_trace_pos[RDS_MSG_RX_DGRAM_TRACE_MAX];
/usr/include/linux/rds.h:203:2: error: unknown type name 'u8'
  u8 rx_traces;
/usr/include/linux/rds.h:204:2: error: unknown type name 'u8'
  u8 rx_trace_pos[RDS_MSG_RX_DGRAM_TRACE_MAX];
/usr/include/linux/rds.h:205:2: error: unknown type name 'u64'
  u64 rx_trace[RDS_MSG_RX_DGRAM_TRACE_MAX];

Fixes: 3289025a ("RDS: add receive message trace used by application")
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>