bgpd: fix advertise pip running config

bgpd: fix advertise pip running config

advertise pip running configuration should
display ip followed by mac parameters value as defined
in cli signature.

advertise-pip is enabled by default, when displaying the
running configuration, there is '\n' added after
ip and mac parameters which was not guarded around
the non-default parameters.

Currently, for every bgp vrf instance it ends up
displaying l2vpn address-family section due to
unguarded newline.

running config:
router bgp 6004 vrf vrf1
 !
 address-family l2vpn evpn
 exit-address-family
!

Ticket:CM-26964
Testing Done:

With fix when only 'router bgp 6004 vrf vrf1' configured,
running config looks like:

!
router bgp 6004 vrf vrf1
!

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>