Issue in dialclient discvoery failures

[honglh]

1. the ssdp_search sets the MX value to 10, allowing the device to have upto 10 seconds to respond. Yet, the RESPONSE_TIMEOUT is set to 5 seconds. The wait loop may exit too early.

2. socket descriptors and wait time should be reset on every select() call

3. In ssdp_msearch response, the LOCATION header field is case_insensitive, thus checking against LOCATION may not work all the time (depends on the DIAL server impl). See the spec here where it states

....header fields appearing .... Field names are not case sensitive. 

Please see PR 34