All user modes on channel.  These indicate the user's status on the
    channel.  Some of the modes can be set by channel founder and channel
    operator.  Some modes may be set by users themself.

    #define SILC_CHANNEL_UMODE_NONE            0x00000000 /* Normal user */
    #define SILC_CHANNEL_UMODE_CHANFO          0x00000001 /* channel founder */
    #define SILC_CHANNEL_UMODE_CHANOP          0x00000002 /* channel operator */
    #define SILC_CHANNEL_UMODE_BLOCK_MESSAGES  0x00000004 /* messages blocked */
    #define SILC_CHANNEL_UMODE_BLOCK_MESSAGES_USERS  0x00000008 /* Block messages
                                                                   from normal
                                                                   users */
    #define SILC_CHANNEL_UMODE_BLOCK_MESSAGES_ROBOTS 0x00000010 /* Block messages
                                                                   from robots */
    #define SILC_CHANNEL_UMODE_QUIET           0x00000020 /* user is quiet */