virQEMUDriverConfigLoadSpecificTLSEntry: Split up fetching of server-only config...

virQEMUDriverConfigLoadSpecificTLSEntry: Split up fetching of server-only config options

The '*_tls_x509_verify' options are relevant only when we are going to
expose a server socket as client sockets always enable verification.

Split up the macro to separate the common bits from the server bits so
that when we'll later extend support of 'nbd' and 'vxhs' disks which are
client only we can reuse the existing macros.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>