Rename cavl.h to _canard_cavl.h to avoid collisions

[pavel-kirienko]

The bundled cavl distribution can be accidentally included instead of the original cavl.h, this bears inconveniences with dependency management.

libcanard/libcanard/cavl.h

Line 1 in db87ea3

/// Source: https://github.com/pavel-kirienko/cavl