bgpd: fix show bgp neighbor routes for labeled-unicast

bgpd: fix show bgp neighbor routes for labeled-unicast

bgp_show_neighbor_route() was rewriting safi from LU to uni
before checking if the peer was enabled for LU.  This resulted
in the peer's address-family check looking for unicast, which
would always fail for LU peers since unicast + LU are
mutually-exclusive AFIs.
This moves this safi reassignment after the peer AFI check,
ensuring that the peer's address-family check looks for LU
while the call to bgp_show() still uses uni.

-- highlights from manual testing

config:

router bgp 2
 neighbor 1.1.1.1 remote-as external
 neighbor 1.1.1.1 disable-connected-check
 neighbor 1.1.1.1 update-source 2.2.2.2
 !
 address-family ipv4 unicast
  no neighbor 1.1.1.1 activate
 exit-address-family
 !
 address-family ipv4 labeled-unicast
  neighbor 1.1.1.1 activate
 exit-address-family

before:

spine01# show bgp ipv4 unicast neighbors 1.1.1.1 routes
% No such neighbor or address family
spine01# show bgp ipv4 labeled-unicast neighbors 1.1.1.1 routes
% No such neighbor or address family

after:

spine01# show bgp ipv4 unicast neighbors 1.1.1.1 routes
% No such neighbor or address family
spine01# show bgp ipv4 label neighbors 1.1.1.1 routes
BGP table version is 1, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, = multipath,
              i internal, r RIB-failure, S Stale, R Removed
Origin codes: i - IGP, e - EGP, ? - incomplete
   Network          Next Hop            Metric LocPrf Weight Path
*> 11.11.11.11/32   1.1.1.1                  0             0 1 i
Displayed  1 routes and 1 total paths

Signed-off-by: Trey Aspelund <taspelund@cumulusnetworks.com>