netdev-dpdk: Fix thread_is_pmd() symbol conflict.

netdev-dpdk: Fix thread_is_pmd() symbol conflict.

DPDK build was broken after commit 2f8932e8403a ("poll: Suppress logging
for pmd threads.") due to the following error:

lib/netdev-dpdk.c:245:13: error: static declaration of ‘thread_is_pmd’
follows non-static declaration
lib/ovs-thread.h:526:6: note: previous declaration of ‘thread_is_pmd’
was here

The version used in this file operates in the fastpath, so it cannot
switch to using the newly introduced version; the new version lives
outside of the dpdk portions of OVS so its implementation cannot be
shared with this function. Rename it to resolve the conflict.

Fixes: 2f8932e8403a ("poll: Suppress logging for pmd threads.")
Suggested-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Joe Stringer <joe@ovn.org>
Acked-by: Flavio Leitner <fbl@sysclose.org>