pcu_l1_if_phy: fix API function names

The functions l1if_open_pdch and l1if_close_pdch have a misleading
naming since what they actually do is opening and closing the TRX since
they return and accept a context (obj) that is valid for a whole TRX.
This also explains why the other functions accept a timeslot as
parameter in addition to the context. Let's rename those functions so
that it is clear what they do.

Related: OS#6022
Change-Id: I395a60b2fba39bac4facec78989bac20f0cef0d3
diff --git a/src/pcu_l1_if_phy.h b/src/pcu_l1_if_phy.h
index 7eba5cc..08b7d23 100644
--- a/src/pcu_l1_if_phy.h
+++ b/src/pcu_l1_if_phy.h
@@ -4,9 +4,9 @@
 #include <osmocom/core/gsmtap_util.h>
 
 int l1if_init(void);
-void *l1if_open_pdch(uint8_t bts_nr, uint8_t trx_no, uint32_t hlayer1, struct gsmtap_inst *gsmtap);
+void *l1if_open_trx(uint8_t bts_nr, uint8_t trx_no, uint32_t hlayer1, struct gsmtap_inst *gsmtap);
 int l1if_connect_pdch(void *obj, uint8_t ts);
 int l1if_pdch_req(void *obj, uint8_t ts, int is_ptcch, uint32_t fn, uint16_t arfcn, uint8_t block_nr, uint8_t *data,
 		  uint8_t len);
 int l1if_disconnect_pdch(void *obj, uint8_t ts);
-int l1if_close_pdch(void *obj);
+int l1if_close_trx(void *obj);