oml: fix oml_mo_tx_sw_act_rep(): do not allocate FOM header twice

This redundant call to msgb_put() appends five '00'O octets to the
"Software Activated Report" message, so they look like an unknown
attribute(s). I accidentally noticed this in Wireshark.

Change-Id: I7377575135f4a154572891d1b5b39ff814b97f38

src/common/oml.c

@@ -472,7 +472,6 @@ int oml_mo_tx_sw_act_rep(const struct gsm_abis_mo *mo)
 	if (!nmsg)
 		return -ENOMEM;
 
-	msgb_put(nmsg, sizeof(struct abis_om_fom_hdr));
 	return oml_mo_send_msg(mo, nmsg, NM_MT_SW_ACTIVATED_REP);
 }