Allowed IP for "Host based virtual hosting".

I solved it by using a 'Data Group' that corresponds with the name of the pool.

Also added 'X-Forwarded-For' to be used for better logging on the webservers since we use SNAT.

when HTTP_REQUEST {
    set xff 0
    foreach x [HTTP::header names] {
        if { [string tolower $x] equals "x-forwarded-for" } {
            set xff 1
            HTTP::header remove $x
            HTTP::header insert X-Forwarded-For [IP::client_addr]
        }
    }   
    if { $xff == 0 } {
        HTTP::header insert X-Forwarded-For [IP::client_addr]
    }
    set HOST [HTTP::host]
    if {[catch {pool "P_EXT_$HOST"}] || [scan [HTTP::host] {%d.%d.%d.%d} 0 0 0 0] == 4}{
        reject
    }
    else {
        if {[class exists "DG_EXT_$HOST"] } {
            if {![class match [IP::client_addr] eq "DG_EXT_$HOST"]} {
                reject
            } else {
                pool "P_EXT_$HOST"
            }
        } else {
            pool "P_EXT_$HOST"
        }
    }
}