r355677 requires that vop_stdioctl() be global so it can be called from NFS.

r355677 modified the NFS client so that it does lseek(SEEK_DATA/SEEK_HOLE)
for NFSv4.2, but calls vop_stdioctl() otherwise. As such, vop_stdioctl()
needs to be a global function.

Missed during the code merge for r355677.