fr: Begin with a GRE/FrameRelay test due the recent regression

The framerelay code is seldomly used and the socket clean ups introduced
a regression. Create a testcase that will work as a user not having the
right capabilities to create raw sockets.

We have to make sure that this test is working even when not ran as root.
The easiest way to do this is to provide our own socket implementation.
This is done with dlopen/dlsym to convert the raw socket request to an UDP
one.
6 files changed