Can't add route with a nexthop of a PortChannel

[DavidZagury]

Description

We no longer can add routes with a nexthop of a PortChannel.
This was possible until the refactor of add/del route functions in this PR - [config]Static routes to config_db (sonic-net/sonic-utilities#1534)

Steps to reproduce the issue:

1. config portchannel add PortChannel0001
2. sudo config route add prefix 20.0.0.1/32 nexthop PortChannel0001

Describe the results you received:

Command fails with error:
Error: ip address is not valid.

Describe the results you expected:

Command succeed and route added successfully.
Route should be appear in "show ip route" output.

Additional information you deem important (e.g. issue happens only occasionally):

This was possible until the refactor of add/del route functions in this PR - [config]Static routes to config_db (sonic-net/sonic-utilities#1534)

[d-dashkov]

Started looking into it

[DavidZagury]

@prsunny the pr that was merged is not enough to fix this issue, we still need to merge sonic-net/sonic-utilities#1857