move the SIOCDELRT and SIOCADDRT compat_ioctl handlers v3

[Christoph Hellwig]

Hi Dave,

this series moves the compat_ioctl handlers into the protocol handlers,
avoiding the need to override the address space limited as in the current
handler.

Changes since v3:
 - moar variable reordering

Changes since v1:
 - reorder a bunch of variable declarations