userspace/snmpd: (no tech change) rename fields in the wrsPortStatusTable_s

Rename fields in the struct wrsPortStatusTable_s to reflect SNMP objects'
names.

link_up -> wrsPortStatusLink
port_mode -> wrsPortStatusConfiguredMode
port_locked -> wrsPortStatusLocked
sfp_vn[16] -> wrsPortStatusSfpVN[16]
sfp_pn[16] -> wrsPortStatusSfpPN[16]
sfp_vs[16] -> wrsPortStatusSfpVS[16]
sfp_in_db -> wrsPortStatusSfpInDB
sfp_GbE -> wrsPortStatusSfpGbE
sfp_error -> wrsPortStatusSfpError
ptp_tx_count -> wrsPortStatusPtpTxFrames
ptp_rx_count -> wrsPortStatusPtpRxFrames

Signed-off-by: Adam Wujek <adam.wujek@cern.ch>