Merge pull request #1395 in SNORT/snort3 from offload_mime_decode to master

Merge pull request #1395 in SNORT/snort3 from offload_mime_decode to master

Squashed commit of the following:

commit 3922aab0afd5e880353a70281d166a2d2516de6d
Author: Bhagya Tholpady <bbantwal@cisco.com>
Date:   Tue Oct 23 13:42:17 2018 -0400

    delete commented lines

commit 2cdc9ca78a9527636f566146802c6168d3509436
Author: Bhagya Tholpady <bbantwal@cisco.com>
Date:   Mon Oct 22 15:24:50 2018 -0400

    allocate buffer only once per mime context data

commit d1d11e4e669d38f0c06165e6e1af25c62f6c0704
Author: Bhagya Tholpady <bbantwal@cisco.com>
Date:   Fri Oct 19 14:34:23 2018 -0400

    changes per code review

commit 622759823ffb87f6fabe7f1a381204370463a4a7
Author: Bhagya Tholpady <bbantwal@cisco.com>
Date:   Wed Oct 17 23:45:25 2018 -0400

    mime: move the decode buffer used by mime attachments to mime context data