net: ipc_router: Do not allow change of default security rule

Default security rule is freed while it is being used to check
security permission in ipcrtr send api. This results in use
after free case.

Default security rule should not be changed, removing the code
to change default rule from user space.

CRs-Fixed: 2591650
Change-Id: I08788102a0748b6bc72cb3c77b46de2d65ede91d
Signed-off-by: Deepak Kumar Singh <deesin@codeaurora.org>