Update Couchbase dissector:

* Register new commands:
    * 0x5c: DCP_NOOP
    * 0x5d: DCP_BUFFER_ACKNOWLEDGEMENT
    * 0x5e: DCP_CONTROL
    * 0x5f: DCP_RESERVED4

Change-Id: I22d8eb8f6628e07b2e2ab2bc137688329eead1be
Reviewed-on: https://code.wireshark.org/review/5385
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>