e1_input.h: add missing extern for value string arrays
e1_input.h: add missing extern for value string arrays

Mark two value string arrays as extern, so symbols aren't created for
each source file that includes the headers.

Tweaked-by: nhofmeyr (commit log)
Signed-off-by: Arran Cudbard-Bell <ea6818f5764ad0ddce21d259fc2be873b00f43c7@freeradius.org>
Change-Id: Iebf4b3922a48ca2cc20d478aba06224dd89d38cb

osmocom/libosmo-abis,osmocom/libosmo-abis,osmocom/libosmo-abis