Sougatab,
There's no option to let you just import the avatar during login. However, there's a pretty easy modification you can try that will force the user's avatar to be updated. Please understand that it will overwrite the user's avatar even if they already have one set.
If you'd like to try it, please edit the /plugins/jfbcprofiles/jomsocial/jomsocial.php file. Around line 63, you'll see the jfbcProfilesOnLogin function. In that function at the very bottom, add the line below right before the closing '}' mark:
$this->migrateSocialAvatarToProfile($joomlaId, $fbUserId);
Test, a lot, and make sure it works how you expect.
Hope that helps, but if not, let us know!
Thanks,
Alex