Fix introducing osmocom speficic OML attributes

Rename NM_ATT_O_REDUCEPOWER to NM_ATT_OSMO_REDUCEPOWER, which
makes it more clear that this is an osmcoom specific attribute.

Also, we cannot simply overload 0x01 as an already defined OML
attribute.  The problem is quite simple: When we use abis_nm_att_tlvdef
during the TLV parse, 0x01 will match to NM_ATT_ABIS_CHANNEL,
which is defined as { TLV_TYPE_FIXED, 3 }.

So instead, we need to introduce a new abis_nm_osmo_att_tlvdef[],
which has to be patched into abis_nm_att_tlvdef[] by the means of
tlv_def_patch(), exactly how we do it for bs-11 and nanobts specific
attributes.

I'm using 0xfe for the attribute, as 0xfe doesn't overlap with the IPA
specific attribues (and we might want to combine/merge the 12.21 plus
IPA plus osmocom spefici attributes)
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 3c5025d..cab4fc4 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -10,6 +10,7 @@
 abis_nm_nack_cause_name;
 abis_nm_nack_name;
 abis_nm_att_tlvdef;
+abis_nm_osmo_att_tlvdef;
 abis_nm_obj_class_names;
 abis_nm_opstate_name;
 abis_nm_nacks;