Problem:
After networking restart, staticd unregistered the nexthop
but failed to register the nexthop again, which caused the
nexthop to remain inactive in zebra for static route.

Fix:
Call to static_zebra_nht_register() from static_install_path() was
removed in 3c05d53. Adding it back
so that staticd can register the nexthop for static routes.

Testing:
After networking restart trigger on h1:

Before fix:
```
h1# show ipv6 route vrf vrf1012
Codes: K - kernel route, C - connected, L - local, S - static,
       R - RIPng, O - OSPFv3, I - IS-IS, B - BGP, N - NHRP,
       T - Table, A - Babel, D - SHARP, F - PBR, f - OpenFabric,
       t - Table-Direct, Z - FRR,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

VRF vrf1012:
S   ::/0 [1/0] via 2003:7:2::1, swp1.2 inactive, weight 1, 00:00:39
K>* ::/0 [255/8192] unreachable (ICMP unreachable) (vrf default), 00:00:39
L * 2000:9:12::3/128 is directly connected, vrf1012, 00:00:39
C>* 2000:9:12::3/128 is directly connected, vrf1012, 00:00:39
C>* 2003:7:2::/125 is directly connected, swp1.2, 00:00:37
L>* 2003:7:2::3/128 is directly connected, swp1.2, 00:00:37
C>* fe80::/64 is directly connected, swp1.2, 00:00:37
h1#
```

After fix:
```
h1# show ipv6 route vrf vrf1012

Codes: K - kernel route, C - connected, L - local, S - static,
       R - RIPng, O - OSPFv3, I - IS-IS, B - BGP, N - NHRP,
       T - Table, A - Babel, D - SHARP, F - PBR, f - OpenFabric,
       t - Table-Direct, Z - FRR,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

VRF vrf1012:
S>* ::/0 [1/0] via 2003:7:2::1, swp1.2, weight 1, 00:00:15
K * ::/0 [255/8192] unreachable (ICMP unreachable) (vrf default), 00:00:17
L * 2000:9:12::3/128 is directly connected, vrf1012, 00:00:17
C>* 2000:9:12::3/128 is directly connected, vrf1012, 00:00:17
C>* 2003:7:2::/125 is directly connected, swp1.2, 00:00:15
L>* 2003:7:2::3/128 is directly connected, swp1.2, 00:00:15
```

Signed-off-by: Pooja Jagadeesh Doijode <pdoijode@nvidia.com>