lib, bgpd: Convert frr_pthread_set_name to only cause it to set os name of the thread

lib, bgpd: Convert frr_pthread_set_name to only cause it to set os name of the thread

The current invocation of frr_pthread_set_name was causing it reset the os_name.
There is no need for this, we now always create the pthread appropriately
to have both name and os_name.  So convert this function to a simple
call through of the pthread call now.

Before(any of these changes):
sharpd@robot ~/frr1> ps -L -p 16895
  PID   LWP TTY          TIME CMD
16895 16895 ?        00:01:39 bgpd
16895 16896 ?        00:00:54
16895 16897 ?        00:00:07 bgpd_ka

After:
sharpd@donna ~/frr1> ps -L -p 1752
  PID   LWP TTY          TIME CMD
 1752  1752 ?        00:00:00 bgpd
 1752  1753 ?        00:00:00 bgpd_io
 1752  1754 ?        00:00:00 bgpd_ka

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>