uridecodebin, urisourcebin: fix buffering for ssh:// URIs

uridecodebin, urisourcebin: fix buffering for ssh:// URIs

Protocols that are in the stream_uris list should always
be streams, no matter what they respond to the scheduling
query. The flag in the scheduling query is just another
way to declare something that needs buffering without the
whitelist, the absence of the flag shouldn't make us ignore
our known protocol list.

Also set is_stream always to a boolean and not a mask value.