gtphub: Make the two setter static as well

Same as with the previous gtphub commit. Make these static to deal
with the new semantic of inline in gcc5.
diff --git a/openbsc/src/gprs/gtphub.c b/openbsc/src/gprs/gtphub.c
index fcb0715..e8bd3ae 100644
--- a/openbsc/src/gprs/gtphub.c
+++ b/openbsc/src/gprs/gtphub.c
@@ -964,14 +964,14 @@
 	pp->ref_count--;
 }
 
-inline void set_seq(struct gtp_packet_desc *p, uint16_t seq)
+static inline void set_seq(struct gtp_packet_desc *p, uint16_t seq)
 {
 	OSMO_ASSERT(p->version == 1);
 	p->data->gtp1l.h.seq = hton16(seq);
 	p->seq = seq;
 }
 
-inline void set_tei(struct gtp_packet_desc *p, uint32_t tei)
+static inline void set_tei(struct gtp_packet_desc *p, uint32_t tei)
 {
 	OSMO_ASSERT(p->version == 1);
 	p->data->gtp1l.h.tei = hton32(tei);