common/iavf: support eCPRI protocol header fields

common/iavf: support eCPRI protocol header fields

Add eCPRI header and its field selectors, including MSG_TYPE, PCID
and RTCID. Since the offset of PCID is same as RTCID, we just add one
MACRO for these two fields. For MSG Type 0, ecpriRtcid/ecpriPcid field
within the eCPRI header will be extracted to Field Vector for FDIR and
RSS.

SPEC for eCPRI:
http://www.cpri.info/downloads/eCPRI_v_2.0_2019_05_10c.pdf

Signed-off-by: Junfeng Guo <junfeng.guo@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>