build: fix 32-bit build of admin

build: fix 32-bit build of admin

We can't guarantee which 64-bit type will be used in an RPC struct;
while %lu worked on 64-bit Linux, that won't always be the type
used on all 64-bit platforms; and certainly is not right for 32-bit:

admin.c: In function 'adminDispatchClientGetInfo':
admin.c:265:25: error: format '%lu' expects argument of type 'long unsigned int', but argument 7 has type 'uint64_t {aka long long unsigned int}' [-Werror=format=]

Signed-off-by: Eric Blake <eblake@redhat.com>