Disable AES-CCM test

See
  - https://github.com/pyca/cryptography/issues/2968 (discussion)
  - https://github.com/pyca/cryptography/issues/1141 (older)

.travis/test.sh

@@ -16,6 +16,12 @@ fi
 if [ "$TEST_COMBINED_MODES" != "yes" ]
 then
   UT_FLAGS+=" -K combined_modes"
+else
+    # AES-CCM not implemented yet in Cryptography
+    # See
+    #  - https://github.com/pyca/cryptography/issues/2968
+    #  - https://github.com/pyca/cryptography/issues/1141
+  UT_FLAGS+=" -K combined_modes_ccm"
 fi
 
 if python --version 2>&1 | grep -q PyPy

test/ipsec.uts

@@ -2521,7 +2521,7 @@ assert(d == p)
 
 #######################################
 = IPv4 / ESP - Tunnel - AES-CCM - NULL
-~ combined_modes
+~ combined_modes combined_modes_ccm
 
 p = IP(src='1.1.1.1', dst='2.2.2.2')
 p /= TCP(sport=45012, dport=80)