[e1] Enable dumping of LAPD frames again

Kill mi_set_pcap_fd from the header, introduce e1_set_pcap_fd
and call it from bsc_hack.c. Hook into abis_rsl_sendmsg and
_abis_nm_sendmsg for sending and e1inp_rx_ts for reading. It compiles
and should not cause a regression.
diff --git a/src/bsc_hack.c b/src/bsc_hack.c
index 6967afa..ac109f1 100644
--- a/src/bsc_hack.c
+++ b/src/bsc_hack.c
@@ -927,7 +927,6 @@
 
 static void create_pcap_file(char *file)
 {
-#if 0
 	mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
 	int fd = open(file, O_WRONLY|O_TRUNC|O_CREAT, mode);
 
@@ -936,10 +935,7 @@
 		return;
 	}
 
-	mi_set_pcap_fd(fd);
-#else
-	fprintf(stderr, "PCAP support currently disabled!!\n");
-#endif
+	e1_set_pcap_fd(fd);
 }
 
 static void print_usage()