www/linux-*-flashplugin11: convert ALSA to option, but off by default

ALSA output in Flash is fragile and doesn't work without the major
linulator update currently baking in dchagin's lemul branch.   While
waiting for that change, current ALSA to a disabled-by-default option.

PR:		195416
Submitted by:	Jan Beich
Approved by:	Continuation of recent work


git-svn-id: svn+ssh://svn.freebsd.org/ports/head@373458 35697150-7ecd-e111-bb59-0022644237b5
Do not use DRI2 as we did not port vboxvideo.ko for DRM2/KMS yet.

PR:		194324


git-svn-id: svn+ssh://svn.freebsd.org/ports/head@373459 35697150-7ecd-e111-bb59-0022644237b5