yappcap.pyx: Resolve some cython warnings.

Resolves 2 warnings when running setup.py:

* `FutureWarning: Cython directive 'language_level' not set, using 2 for
   now (Py2). This will change in a later release!`
* `Non-trivial type declarators in shared declaration (e.g. mix of
  pointers and values). Each pointer declaration should be on its own line.`

Author: seanbright

Diff for: yappcap.pyx

@@ -1,4 +1,4 @@
-#cython: embedsignature=True
+#cython: language_level=3, embedsignature=True
 #distutils: libraries = pcap
 include "definitions.pxi"
 from pcap cimport *
@@ -809,7 +809,8 @@ def lib_version():
 
 def findalldevs():
     """Return a list of available PcapInterfaces"""
-    cdef pcap_if_t *interfaces, *it
+    cdef pcap_if_t *interfaces
+    cdef pcap_if_t *it
     cdef char errbuf[PCAP_ERRBUF_SIZE]
     cdef int res = pcap_findalldevs(&interfaces, errbuf)
     cdef list result = list()