Use svm_fifo_peek in http_read_message and advance rx fifo head by
amount of bytes send to app, since not always you won't or can't
send all bytes.
Type: improvement
Change-Id: I84348c9df5c77ba386c9738a754295bb9ea0f7ef
Signed-off-by: Matus Fabian <matfabia@cisco.com>