Integer overflow in l64_setdisklabel partition bounds check: p_boffset+p_bsize wraparound bypasses ENOSPC

Summary

l64_setdisklabel(:304) checks p_boffset+p_bsize>d_total_size but no wraparound guard. 32-bit code has explicit p_offset+p_size<p_offset check(l32_fixlabel:596). p_boffset=0x1000,p_bsize=0xFFFFFFFFFFFFF000 wraps to 0x0 bypassing check. Privileged caller can install oversized partition enabling cross-partition I/O.