Hello,

The "network-interface-names" test from tests/syscalls.scm fails if a
network interface alias is configured.

I.e. this command:

  ip addr add 127.0.0.2/8 dev lo label lo:lcat

causes the interface to show up in (network-interface-names), but not
(all-network-interface-names), breaking the test.

I could not find a procfs file that displays network aliases, so ISTM
we either need to add syscalls to check IFLA_IFALIAS, or simply ignore
interfaces with a colon (which seems to be required).

This patch does the latter and makes the test succeed: