ethdev: fix string length in name comparison

ethdev: fix string length in name comparison

The current code compares two strings upto the length of 1st string
(searched name). If the 1st string is prefix of 2nd string (existing name),
the string comparison returns the port_id of earliest prefix matches.
This patch fixes the bug by using strcmp instead of strncmp.

Fixes: 9c5b8d8b9fe ("ethdev: clean port id retrieval when attaching")
Cc: stable@dpdk.org
Signed-off-by: Mohammad Abdul Awal <mohammad.abdul.awal@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>