package/vde2: fix build issue with gcc 7.x

Like for dieharder package [1], add static to inline functions.
https://git.buildroot.net/buildroot/commit/?id=21133ada326c87627f7bdee4493d8086587c3cca

Fixes:
http://autobuild.buildroot.net/results/ed9/ed9abb1aed2ae87971ae119f4bca83cbf9861466
http://autobuild.buildroot.net/results/2a1/2a1f73bfaf7097d42165d5c5f6c24d1aad72c929



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>