add USBTMC_IOCTL_CONFIG_TERMCHAR to control TermChar handling
for next read(). Controls field 'TermChar' and Bit 1 of field
'bmTransferAttributes' of REQUEST_DEV_DEP_MSG_IN BULK-OUT header.

Allows enabling/disabling of terminating a read on reception of
term_char individually for each read request.
Reviewed-by: NSteve Bayless <steve_bayless@keysight.com>
Tested-by: NDave Penkler <dpenkler@gmail.com>
Signed-off-by: NDave Penkler <dpenkler@gmail.com>
Signed-off-by: NGuido Kiener <guido.kiener@rohde-schwarz.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>