srs_enb: Make num_prb a config parameter

Change-Id: I336e71f53556596050cf3eb55a7810a009dbf7a8
diff --git a/src/osmo_gsm_tester/templates/srsenb.conf.tmpl b/src/osmo_gsm_tester/templates/srsenb.conf.tmpl
index 2006832..f040156 100644
--- a/src/osmo_gsm_tester/templates/srsenb.conf.tmpl
+++ b/src/osmo_gsm_tester/templates/srsenb.conf.tmpl
@@ -28,7 +28,7 @@
 mme_addr = ${enb.mme_addr}
 gtp_bind_addr = ${enb.addr}
 s1c_bind_addr = ${enb.addr}
-n_prb = 50
+n_prb = ${enb.num_prb}
 #tm = 4
 #nof_ports = 2