Fix network namespace setup script

At least my machine was generating IDs that were to long and any test
that required networking wouldn't work. This patch restricts the
namespace names to 4 digits.

Signed-off-by: Lee Keitel <lee@keitel.xyz>

tests/ns.sh

@@ -75,13 +75,13 @@ trap nsfinish EXIT
 
 echo " * Setting up namespaces..."
 set -e
-NSNAME1="ocserv-c-tmp-$$"
-NSNAME3="ocserv-c-2-tmp-$$"
-NSNAME2="ocserv-s-tmp-$$"
-ETHNAME1="oceth-c$$"
-ETHNAME2="oceth-s$$"
-ETHNAME3="oceth-c-2$$"
-ETHNAME4="oceth-s-2$$"
+NSNAME1="ocserv-c-tmp-${$:0:4}"
+NSNAME3="ocserv-c-2-tmp-${$:0:4}"
+NSNAME2="ocserv-s-tmp-${$:0:4}"
+ETHNAME1="oceth-c${$:0:4}"
+ETHNAME2="oceth-s${$:0:4}"
+ETHNAME3="oceth-c-2${$:0:4}"
+ETHNAME4="oceth-s-2${$:0:4}"
 
 ${IP} netns add ${NSNAME1}
 ${IP} netns add ${NSNAME2}