Update Apache MINA to 2.1.2

Apache MINA 2.1.2 has been released - http://mail-archives.apache.org/mod_mbox/mina-users/201904.mbox/%3CCAG8%3DFRjFRgTTXMM-guPKCJ7Mun2EvD2G8gezjTM3dZuu6gtjZQ%40mail.gmail.com%3E

The release notes are somewhat vague, but do mention;

This is a bug fix release for MINA 2.1.1. it fixes an issue for
applications using SSL/TLS, which will stall waiting on a WriteFuture
because it does not get signaled when the message has been fully sent.

It is unlikely that Openfire is affected by this, but an updated is probably worthwhile nonetheless.