github: Use nmap-ncat instead of netcat-openbsd.

There are some bugs in the netcat-openbsd version shipped with Ubuntu
20.04.  Switch to nmap-ncat to avoid system tests that will be added
by upcoming commits fail in CI.

One example:

1. Start a TCP connection from IP1:port-x to IP2:port-y.
2. Start a TCP connection from IP1:port-x to IP3:port-z.

netcat-openbsd fails with:
  nc: bind failed: Address already in use

Acked-by: Mark D. Gray <mark.d.gray@redhat.com>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
Signed-off-by: Numan Siddique <numans@ovn.org>
(cherry picked from commit f6bd743)

.github/workflows/test.yml

@@ -13,7 +13,7 @@ jobs:
       dependencies: |
         automake libtool gcc bc libjemalloc2 libjemalloc-dev    \
         libssl-dev llvm-dev libelf-dev libnuma-dev libpcap-dev  \
-        selinux-policy-dev
+        selinux-policy-dev ncat
       m32_dependecies: gcc-multilib
       CC:          ${{ matrix.compiler }}
       LIBS:        ${{ matrix.libs }}
@@ -76,6 +76,9 @@ jobs:
     - name: update APT cache
       run:  sudo apt update
 
+    - name: remove netcat-openbsd
+      run:  sudo apt remove -y netcat-openbsd
+
     - name: install required dependencies
       run:  sudo apt install -y ${{ env.dependencies }}