compat/freebsd32: set uio_rw for trailer's uio in freebsd32_sendfile()

PR:	297516
Reported by:	asomers
Fixes:	dfad790c8c ("sendfile: stop abusing kern_writev()")
Sponsored by:	The FreeBSD Foundation
MFC after:	3 days

sys/compat/freebsd32/freebsd32_misc.c

@@ -2251,6 +2251,8 @@ freebsd32_do_sendfile(struct thread *td,
 			    hdtr32.trl_cnt, &trl_uio);
 			if (error)
 				goto out;
+			trl_uio->uio_rw = UIO_WRITE;
+			trl_uio->uio_td = td;
 		}
 	}