Enable BIO_DELETE passthru in GELI, so TRIM/UNMAP can work as expected when
GELI is used on a SSD or inside virtual machine, so that guest can tell
host that it is no longer using some of the storage.

Enabling BIO_DELETE passthru comes with a small security consequence - an
attacker can tell how much space is being really used on encrypted device and
has less data no analyse then. This is why the -T option can be given to the
init subcommand to turn off this behaviour and -t/T options for the configure
subcommand can be used to adjust this setting later.

PR: 198863
Submitted by: Matthew D. Fuller fullermd at over-yonder dot net

This commit also includes a fix from Fabian Keil freebsd-listen at
fabiankeil.de for 'configure' on onetime providers which is not strictly
related, but is entangled in the same code, so would cause conflicts if
separated out.