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