security/openvpn-devel: upgrade port to git commit e778a6fd26d (2022-12-01)

this commit is also 2.6_beta1.

contains a good number of bugfixes and minor improvements

user visible changes since last port upgrade

• binary identifies itself as "2.6_beta1"
• client reconnect in p2p TLS mode works now with DCO enabled (on FreeBSD 14)
• more robust handling of cipher negotiation issues in p2p TLS mode
• supports server-pushable "tun-mtu" now
• support DCO with AES-192-GCM on sufficiently-new FreeBSD 14 kernels