Rx: Fix socket() handling so errors are properly detected

Rx: Fix socket() handling so errors are properly detected

socket() returns an osi_socket which on Windows is an
unsigned type (HANDLE).  Therefore, tests of osi_socket < 0
will never identify when the INVALID_SOCKET value is returned.
On Windows, the OSI_NULLSOCKET is assigned to INVALID_SOCKET.
Replace all comparisons of (osi_socket < 0) with
(osi_socket == OSI_NULLSOCKET) as a means of detecting errors.

In addition, do not pass socket() the protocol value 0 when
IPPROTO_UDP is what is desired.

Finally, perror() on Windows never reports any error from Winsock.
perror() is a CRT function.  To get the real socket error
WSAGetLastError() must be called and its value be written to
stderr.

Change-Id: Ibc392eeb733851f56dbc7398cb252a4753b95275
Reviewed-on: http://gerrit.openafs.org/3027
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>