staging: unisys: refactor DIAG_CHANNEL_PROTOCOL_HEADER

Get rid of the typedef and use struct diag_channel_protocol_header instead. Fix
CamelCase member names and update references and comments.

DiagLock => diag_lock
IsChannelInitialized => channel_initialized
Reserved => reserved
SubsystemSeverityFilter => subsystem_severity_filter

Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>