net: Change the layout of structure trace_event_raw_fib_table_lookup

There is an unalignment access about the structure
'trace_event_raw_fib_table_lookup'.

In include/trace/events/fib.h, there is a memory operation which casting
the 'src' data member to a pointer, and then store a value to this
pointer point to.

p32 = (__be32 *) __entry->src;
*p32 = flp->saddr;

The offset of 'src' in structure trace_event_raw_fib_table_lookup is not
four bytes alignment. On some architectures, they don't permit the
unalignment access, it need to pay the price to handle this situation in
exception handler.

Adjust the layout of structure to avoid this case.

Fixes: 9f323973 ("net/ipv4: Udate fib_table_lookup tracepoint")
Signed-off-by: Zong Li <zong@andestech.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>