nfc: uapi: use kernel size_t to fix user-space builds

Fix user-space builds if it includes /usr/include/linux/nfc.h before
some of other headers:

  /usr/include/linux/nfc.h:281:9: error: unknown type name ‘size_t’
    281 |         size_t service_name_len;
        |         ^~~~~~

Fixes: d646960f

 ("NFC: Initial LLCP support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>