Allow more time for DTLS interop tests with proxy

Sometimes see false positives on buildbot, trying to avoid that
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 510000a..fab278f 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -3108,7 +3108,7 @@
             -s "Extra-header:" \
             -c "HTTP/1.0 200 OK"
 
-needs_more_time 6
+needs_more_time 8
 run_test    "DTLS proxy: 3d, openssl server, fragmentation" \
             -p "$P_PXY drop=5 delay=5 duplicate=5 protect_hvr=1" \
             "$O_SRV -dtls1 -mtu 768" \
@@ -3117,7 +3117,7 @@
             -s "Extra-header:" \
             -c "HTTP/1.0 200 OK"
 
-needs_more_time 6
+needs_more_time 8
 run_test    "DTLS proxy: 3d, openssl server, fragmentation, nbio" \
             -p "$P_PXY drop=5 delay=5 duplicate=5 protect_hvr=1" \
             "$O_SRV -dtls1 -mtu 768" \
@@ -3137,7 +3137,7 @@
             -c "Extra-header:"
 
 requires_gnutls
-needs_more_time 6
+needs_more_time 8
 run_test    "DTLS proxy: 3d, gnutls server, fragmentation" \
             -p "$P_PXY drop=5 delay=5 duplicate=5" \
             "$G_SRV -u --mtu 512" \
@@ -3147,7 +3147,7 @@
             -c "Extra-header:"
 
 requires_gnutls
-needs_more_time 6
+needs_more_time 8
 run_test    "DTLS proxy: 3d, gnutls server, fragmentation, nbio" \
             -p "$P_PXY drop=5 delay=5 duplicate=5" \
             "$G_SRV -u --mtu 512" \