pam: declare root as sufficient frr pam account

pam: declare root as sufficient frr pam account

https://github.com/FRRouting/frr/pull/11465 enabled account verification,
but the pam config declares rootok as sufficient in authentication only
and not in account verification, what causes warning in the log:

vtysh[3747]: pam_warn(frr:account): function=[pam_sm_acct_mgmt]
             flags=0 service=[frr] terminal=[<unknown>] user=[root]
	     ruser=[<unknown>] rhost=[<unknown>]

Signed-off-by: Marius Tomaschewski <mt@suse.com>