scons: Merge redundant checks for the socket library.

scons: Merge redundant checks for the socket library.

scons can accept more than one library at a time, so lets check for both
at once instead of writing out almost the same check twice.

Change-Id: I82f9bdf59a349e28ca75a615d711051256ec73a4
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40869
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>