packet-http2.c: Do encoding-arg changes (all benign)

For:
- FT_BYTES: Always use just ENC_NA
- integral/floating (other than FT_[U]INT8): Do ENC_NA --> ENC_BIG_ENDIAN

Change-Id: I0885f7d110014cb8a7eba1c1892ed8d0852d076a
Reviewed-on: https://code.wireshark.org/review/4187
Reviewed-by: Bill Meier <wmeier@newsguy.com>