libexec/rc: improve performance of pccard_ether script

Replace "ifconfig -ul" with "ifconfig -n" because netlink-enabled
/sbin/ifconfig utility has sub-optimal performance for listing.

Combined with the commit b1b17432aa1be670564161232d110461a5dde4ce,
these changes mostly eliminate performance regression of the command
"service devd start" for a system having hundreds of network interfaces
created before devd starts, after FreeBSD 14+ switched
/sbin/ifconfig to netlink(4)

PR: 287872
MFC-after: 2 weeks