libexec/rc: MFC: 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

(cherry picked from commit 6d3bc576abbd84f736d917f5bfec4e3fe7e6c125)
(cherry picked from commit 24e8ed535ff673b9ea751c3d3b2a68ef0a29b0e2)