add: [network-connection] Added multiple to layer7-protocol attribute

- As a connection between 2 IP addresses and ports,
  via a given transport layer could potentially
  have more than 1 application protocol

Author: chrisr3d

objects/network-connection/definition.json

@@ -96,6 +96,7 @@
       "description": "Layer 7 protocol of the network connection.",
       "disable_correlation": true,
       "misp-attribute": "text",
+      "multiple": true,
       "sane_default": [
         "HTTP",
         "HTTPS",