BUG/MINOR: ssl: Fix compilation with OpenSSL 1.0.2 (missing ECDSA_SIG_set0)

This function was introduced in OpenSSL 1.1.0. Prior to that, the
ECDSA_SIG structure was public.
This function was used in commit 5a8f02ae "BUG/MEDIUM: jwt: Properly
process ecdsa signatures (concatenated R and S params)".

This patch needs to be backported up to branch 2.5 alongside commit
5a8f02ae.
1 file changed