[vslib] MACsec interface creation fails when send_sci=false

[vikram-nexthop]

Bug Description

MACsec interface creation commands fails on VM/VS with send_sci=false and SCI combination.

admin@VM:~$ sudo ip link add link "eth0" name "macsec_eth1" type macsec  sci 226b54b065000001 encrypt  on  send_sci off cipher GCM-AES-128
RTNETLINK answers: Invalid argument

Steps to Reproduce

Configure MACsec with send_sci=false

Expected Behavior

MACsec interface should be created successfully regardless of send_sci setting.

Root Cause

The current implementation always includes SCI and send_sci parameters in ip link add command.
Linux kernel rejects SCI with send_sci=false combination with invalid argument error drivers/net/macsec.c.

Code Location

sonic-sairedis/vslib/MACsecManager.cpp - create_macsec_egress_sc() function

Proposed Fix

Implement two-step approach:

1. Create interface with send_sci=on to set SCI.
2. Switch to send_sci=off if required.

Impact

Blocks MACsec deployment in scenarios requiring SCI transmission disabled
Affects VM/VS testing environments

Related Issue(s)

sonic-net/sonic-buildimage#12991