tests: refactor. Replace literal constant w/ named constant.

* change literal packet count vlaues from 65 to a named constant of 67.
  (This value was recommended to exercise single, dual, and quad loops)

Change-Id: Ieb1738dddacb8b6ea7fa25883032ac01a98399e1
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>
diff --git a/test/test_mpls.py b/test/test_mpls.py
index 2e0b71f..79f3204 100644
--- a/test/test_mpls.py
+++ b/test/test_mpls.py
@@ -2014,7 +2014,7 @@
                  UDP(sport=1234, dport=1234) /
                  Raw('\xa5' * 100))
 
-        tx0 = pcore * 65
+        tx0 = pcore * NUM_PKTS
         rx0 = self.send_and_expect(self.pg0, tx0, self.pg1)
         payload = pcore[MPLS].payload
 
@@ -2024,7 +2024,7 @@
         #
         # Inject a packet from the customer/L2 side
         #
-        tx1 = pcore[MPLS].payload * 65
+        tx1 = pcore[MPLS].payload * NUM_PKTS
         rx1 = self.send_and_expect(self.pg1, tx1, self.pg0)
 
         self.verify_capture_tunneled_ethernet(rx1, tx1, [VppMplsLabel(42)])
@@ -2100,13 +2100,13 @@
         #
         # now a stream in each direction
         #
-        self.pg1.add_stream(p_cust * 65)
+        self.pg1.add_stream(p_cust * NUM_PKTS)
         self.pg_enable_capture(self.pg_interfaces)
         self.pg_start()
 
-        rx0 = self.pg0.get_capture(65)
+        rx0 = self.pg0.get_capture(NUM_PKTS)
 
-        self.verify_capture_tunneled_ethernet(rx0, p_cust*65,
+        self.verify_capture_tunneled_ethernet(rx0, p_cust*NUM_PKTS,
                                               [VppMplsLabel(42)])
 
         #