Fix M-SEARCH issues in gssdp

[Jens Georg <mail jensge org>]

While running the UPnP certification tool, we came across the following
issues with M-SEARCH replies:

 a) USN + ST don't match (should match the version in M-SEARCH)
 b) gssdp replys to every M-SEARCH that matches the target, even for
higher versions

I fixed both issues in
https://gitorious.org/gupnp/gssdp/merge_requests/6

This also reverts c39bba86c215785afefd16a9eeab1def2556a4e2 which is
wrong according to UPnP arch document. We have at least one confirmation
that fixing a) also fixes the issue that Zeeshan tried to fix with this
commit.

c39bba86c215785afefd16a9eeab1def2556a4e2 also causes failures in UPnP
CTT.

Regards,
	Jens.