file_data: check for signature alproto and flow

file_data: check for signature alproto and flow

Currently the following rule can't be loaded:
alert tcp any any -> any 25 (msg:"SMTP file_data test"; flow:to_server,established; file_data; content:"abc";sid:1;)
and produces the error output:
"Can't use file_data with flow:to_server or from_client with http or smtp."

This checks if the alproto is not http in a signature,
so permits to use flow keyword also.

Issue reported by rmkml.