oml: Make it possible to include the file directly
oml: Make it possible to include the file directly

Fixes:
../../include/osmo-bts/oml.h:8:42: warning: ‘struct gsm_bts’ declared inside parameter list [enabled by default]
 int down_oml(struct gsm_bts *bts, struct msgb *msg);
                                          ^
../../include/osmo-bts/oml.h:8:42: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]
../../include/osmo-bts/oml.h:12:52: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
 int oml_mo_send_msg(struct gsm_abis_mo *mo, struct msgb *msg, uint8_t msg_type);
                                                    ^
../../include/osmo-bts/oml.h:13:31: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
 int oml_mo_opstart_ack(struct gsm_abis_mo *mo);
                               ^
../../include/osmo-bts/oml.h:14:32: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
 int oml_mo_opstart_nack(struct gsm_abis_mo *mo, uint8_t nack_cause);
                                ^
../../include/osmo-bts/oml.h:15:32: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
 int oml_mo_statechg_ack(struct gsm_abis_mo *mo);
                                ^
../../include/osmo-bts/oml.h:16:33: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
 int oml_mo_statechg_nack(struct gsm_abis_mo *mo, uint8_t nack_cause);
                                 ^
../../include/osmo-bts/oml.h:19:29: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
 int oml_mo_state_chg(struct gsm_abis_mo *mo, int op_state, int avail_state);
                             ^
../../include/osmo-bts/oml.h:22:31: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
 void oml_mo_state_init(struct gsm_abis_mo *mo, int op_state, int avail_state);
                               ^
../../include/osmo-bts/oml.h:26:10: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
          int success);
          ^
../../include/osmo-bts/oml.h:29:33: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
 int oml_tx_state_changed(struct gsm_abis_mo *mo);
                                 ^
../../include/osmo-bts/oml.h:31:33: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
 int oml_mo_tx_sw_act_rep(struct gsm_abis_mo *mo);
                                 ^
../../include/osmo-bts/oml.h:36:4: warning: ‘struct gsm_abis_mo’ declared inside parameter list [enabled by default]
    uint8_t cause);

osmocom/osmo-bts,geosphere/osmo-bts,geosphere/osmo-bts,telenoobie/osmo-bts,geosphere/osmo-bts,telenoobie/osmo-bts,telenoobie/osmo-bts,osmocom/osmo-bts,geosphere/osmo-bts,osmocom/osmo-bts,telenoobie/osmo-bts