during a shuffling of the CI directories, CI/travis/check_kernel.sh was removed.

09c0898#diff-a37e1affdcbdf72de04029402805155c7cafde708598281cda8a923c0607e461

now, there is no checking to make sure the libiio enum and struct matches the kernel, which will eventually lead to some problems...

Add the file back:
https://github.com/analogdevicesinc/libiio/blob/5b9ef36ebccfc82533c5dd949b19f8180a751952/CI/travis/check_kernel.sh

and plumb it into the CI, so it works and checks things once per PR. (not on every CI client).

-Robin