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: d646960f7986 ("NFC: Initial LLCP support")
Cc: <[e-mail]>
Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/uapi/linux/nfc.h

···
 	__u8 dsap; /* Destination SAP, if known */
 	__u8 ssap; /* Source SAP to be bound to */
 	char service_name[NFC_LLCP_MAX_SERVICE_NAME]; /* Service name URI */;
-	size_t service_name_len;
+	__kernel_size_t service_name_len;
 };
 
 /* NFC socket protocols */